This is a pet peeve of mine. I believe we as divers still have too much the mentality of "sucking it up", "not being a pussy", "it will get better underwater", which in many cases is the wrong attitude.
Specifically when there is an authority imbalance (ie instructor/experienced diver vs beginner) or when a lot has already been invested in the dive by the dive-team it takes a lot of courage to openly state that you want to abort. There is a lot of psychology and peer pressure involved and not always in the way you think. Three personal examples that I have seen/experienced.
Instructor vs student:
The only 2 star instructor of a local CMAS club needs to take one of the final tests for a soon to be AI. It involves a shore dive with a 40m descend, simulate OOA, buddy breath and then assisted ascend. There is peer pressure on the instructor, because he's the only one in the club able to take the test and the student is under time pressure because the official examination is in a couple of weeks. Hence this is the only valable moment to do this test. Instructor forgets his mask, only finds out after getting to the shore. Someone else lends him an ill fitting mask. They descend against current while he keeps flooding his mask/clears, creating a CO² hit. Arriving at 40m he feels extremely uncomfortable, out of breath. It doesn't get better and he thinks he's not getting any gas (while is regulator is working fine) so he goes out of air. He get's the octopus from his student, but he still thinks he's not getting any gas. He bails... the student tries to arrest his ascend but it's still an almost blow up like ascend. I was on the scene and was the first to assist when they came to the surface. Both were ok (after a visit to hospital) and I talked to the instructor a couple of weeks later. He had felt quite bad already (not slept well), but felt peer pressure to do this dive, because the AI to be had invested so much already and she was not going to be ready for the final exam if this test was not done. This decision didn't change when he realised he forgot his mask, or during the descend when it kept flooding. The single idea in his head was "I need to do this for my student".
Team of 3 becomes team of 2, north sea wreck dive:
3 man team signs up for a north sea wreck charter. 2 days before the charter sails one of the team bails because his daughter is ill. The now 2 man team arrives early morning on the boat. Diver A feels a bit queezy, didn't sleep very well, but sucks it up, because north sea diving is always like that (and to be honest it is...). However he forgot his seasickness pills and the ride out is quite choppy. He throws up a couple of times and feels extremely uncomfortable and wants to call the dives (2). However he doesn't do because, this would also mean 2 lost dives for his buddy (remember they are only a team of 2 now), not only lost time, but also lost money. The skipper of the charter states that conditions on the wreck are marvelous, so diver A sucks it up and they dive. Underwater his seasickness improves but he still feels bad, but doesn't call the dive. They finish the dive, get back on board and he has a minor DCS hit. I'm not saying that the DCS hit is linked to him feeling uncomfortable (it was a 50m, 30' bottom time dive so the risk is always there). However because of the hit he told the whole background, which he probably wouldn't have if the dive went as planned. In the end he wanted to abort the dive but felt pressured because a lot was already invested in this dive.
Big cave dive we all felt uneasy about:
So we are doing (for us at the time) a big cave dive, going to 3rd T of Ressel cave (which is about 900m in after about 500m at 50m). Big dubbel sets, 4 stages, scooters and backup scooter. By the time everything is setup, in the water, clicked on, getting to the entrance, going over the plan and keypoints again, equipment check... you have been in the water for some time already. I didn't feel well but didn't say anything. So we start the dive and it all comes down to details for such dives, and from the first couple of meters it felt uneasy, nothing went easy. Clipping of the O² was not easy, putting the leash back on the D ring was a bit of a hassle, scooter in the way...blablabla. First T same story, 2nd drop (50%) same story... we were messy, in eachothers way, and we were losing time. In the end getting to the shaft which would take with scooters and drops about 18-20 min if you are at ease took almost half an hour. Then a teammembers main light broke. Of course we call the dive get back out, leave the dropped stages in (so out with 2 bottom stages). Getting to the surface someone on the surface of our group says he'll lend his main light. By the time we get it and attached, recalculate gas and adjust the plan we are another 30' further so almost 2 hours in cold water. I'm feeling bad about this dive now but I'm not calling it, so much invested you know. Luckily our 3rd team member calls the dive for the exact same reasons as I'm having in my head (not efficient, already long in the water, not feeling totally at ease). That was a very brave thing to do... and us 3 all felt very relieved that he called it. So we dropped everything and just did an easy back gas dive without scooters to collect the dropped deco tanks. No deep cave dive today lads. BIG kudos to our 3rd team member for doing that.
To the OP: Sorry for being long winded. I gave some examples which are why calling a dive is hard (psychologically speaking) and will remain hard, even when you gain experience. But that it's very important to always listen to your "inner voice" and next to that realise that it's a hard thing to do, but in some cases the best thing to do.
This doesn't mean that you should not keep improving, and try to get more comfortable in the water. Of course... but being able to put peer pressure and ego aside and being able to say... I'm not feeling comfortable, I want to call this one is a big thing to learn. Something you have already mastered and will make you a great diver.