I was pretty overweighted in my OW and Ice classes and I was less concerned about that than I was more overwhelmed with the experience of it all. Maybe this is how the OP feels. It took me a full 15 minutes to descend on the first open water dive, and I sucked a ton of air on that one, shortening the dive to 25 minutes. I just wasn't prepared for it. I had good, one-on-one instruction (language barrier aside, she tried....really.) I still suck air. It's worse with my FFM, and I'm getting better, but when everyone else is diving an 80, I'm usually taking a 100 out and we're finishing around the same time.
For my OW it was just being out in the ocean for the first time, at 35 feet deep, knowing there was a long swim up to where I could take my poorly-fitting mask off and breathe normally. Maybe equipment was a minor issue. Maybe I was just scared that as soon as I took my mask off for a swim, I was gonna breathe in through my nose and choke and die at 35 feet deep. It's a lot to go through for a first timer, and I was scared as hell. I still get scared every time something new comes up. There's nothing wrong with that. Fear motivates you to succeed. For diving, I think everyone needs a little fear in the back of their mind to motivate them to compete the tasks necessary to finish the dive on their feet, whether it's climbing up a ladder at the end of the dive or walking up the shore out of the lake. When you get complacent, bad things can happen.
I just finished my AOW in PDC this past December. I was nervous as hell for the first few dives, even though I had been out to the dive site (Jardines) before. This was the PPB dive, so I got through the descent, did the hover, and after a few minutes, I was care free. I saw my first shark on this dive and I didn't even freak out. In fact, I signed up for two shark dives in the next few days.
For my AOW deep dive, I was crazy nervous because I had never gone deeper than 45 feet and the plan was for a 100 foot drift dive at Moc-Che. We back-rolled in and descended quickly, and all I remember was concentrating on checking my air and depth every few seconds, and thinking "if stuff goes pear-shaped, what am I gonna do?" I remember looking up and thinking "that's a lot of water between me and safety" but I trusted my gear, and I trusted my training, and I kept my mind on the task at hand. After a few minutes of worrying (checking depth and air every 30 seconds) I just sat back and enjoyed the ride and everything just clicked. I still checked my gauges once in a while, probably more often than anybody else, but for the most part, I just sat back and enjoyed the dive. The shark dives over the next two days were a piece of cake.
Doing the nav dive, search and recovery and a few fun dives before that helped as I was able to get used to how things worked on the boat again, and I was less concerned about doing something stupid. It gave me time to get properly weighted, and the PPB dive really nailed things down for me. Maybe it'll take a few more dives just to get used to it, OP, but keep diving. Again, do a few pool sessions just to get used to the fact that you're breathing under water. In a few pool sessions I went from 26 lbs of lead to 10 lbs, and I can probably shed some more and dive on 8 lbs if I really wanted to, and I wear a 2.5 mm full suit and do pool sessions in an AL80.
It doesn't take a ton of diving to get used to this. I've done 25 dives and about 10 pool sessions. I've progressed from panicking in a pool to panicking in 3-foot vis water....and now I've decided that I love cave diving and I'm waiting for spring so I can take a sidemount course (partially to help my back........old people problems........partially so I can dive more caves). I actually look forward to diving in limited visibility now because I can challenge myself a little more.