It's easy to feel butterflies about a "first", esp. if you have a lot of time to mull it over in advance and others hype it up. Just take it slow and remember that you are supposed to be having fun. If you definetely aren't having fun anymore, abort the dive. If you are feeling nervous watch your breathing => to an amazing extent you can be calm in you breath calmly (and in turn become stressed if you breath fast and shallow like a stressed person). Pause frequently to breath in with a slow, long, deep motion. Then breath out, once again slowly and easily in a relaxed manner. I usually do that 3x in a row, and only then start considering what I want to do next.
One really nice thing about diving is that you don't need to be scared, or stressed, or "have the taste of blood in your mouth" (as the Finns describe the feeling). If you genuinely aren't happy/aren't having fun, you are not only entirely entitled to abort the dive, but you're actually a smart cookie for doing so.