Hi. Freshman in college here.
First of all, don't be intimidated by other riders at all, especially if you're used to breaking in green ponies, that just shows you can ride anything! I'd include that in the application.
My colleges IHSA team is currently looking for more beginner riders to ride in the beginner classes, so even if you aren't spectacular (Which I'm sure you are) you probably have a chance because they'll probably need a spot in some class somewhere.
I did NOT try out for my schools riding team for two reasons. 1. Cost, almost 1000$ a semester if you factor in everything. That's insane especially when you're in college. Money will become scarce, you'll have to buy books and such.
2. There would be a chance I wouldn't be riding in shows because some people don't get to often. It seemed pointless to join a team and pay so much with the possibility of seeing minimum show time.
Also time will be scarce depending on your major. I'm a science major and the twice daily team workouts at the gym, solo workout once a week, 2 practices and one lesson would simply cram 20 more sardines into an already overflowing can.
These are things to consider, not trying to discourage you because every school is different, possibly cheaper, more ride time, easier schedule flexibility
Keep your option open! I didn't try out for IHSA but my school has a Polo team. It's slightly cheaper than the IHSA team, and is easier on my schedule. I made the team and it is SO SO SO fun! If you for some reason try out for the riding team and don't make it try something else! Of course it's limited by the schools options, but my school also has a dressage team and a western team so definitely keep an open mind you may have options!