Sara. I don't know what your expectations were, but Open Women's racing is a crap shoot. If the big guns show up, it's going to be a long day. Vanderkitten, Tibco, Exergy, development squad or not, those are big guns. You also cannot discount your age versus the kittens. You got a finish, that's actually step #2. So you did well considering this is your first criterium.
Aggressiveness in criteriums is normal at all levels. You don't have to be an animal, but you will want to learn how to take a wheel at will in the field and defend it. It won't always work. I'm a little guy, so sometimes I'd rather let the big monsters have my wheel and find another. It is a skill you will want to work on, and it's best done in a practice race. Are there any weekly practice crits in your area?
I think you found out what it means to start up front. You have to be able to at least dictate the pace if you start up there. If your intention is to sit in and let the race unfold, then start a few rows back in the middle next time, or at the back. The back can actually be safer and better as you can easily move your way to the middle around the riders who are slow to clip in. Make sure that you practice your clip-ins regularly so that you can take advantage of others.
All in all you did just fine, better than I would have expected in your first criterium. Don't be discouraged, just keep at it. Try and find a Women's Cat 3/4 race next. The difference is significant. Once you get to the point where you're finishing in the field, then we can talk about the finer points like cornering, tactics, breaks, etc.