I'd say you're worrying a bit too much. Most people don't get their first choice and it doesn't matter at all. It mostly depends (for me it did) the location (but most residences are within the same area), who your roommate/s are (since you will most likely spend a lot of time with him/her) and maybe your neighbours if they're loud or not.
I think once you fill out that questionnaire it's all up to the computer from there. And most times it does work out. I ended up with a super quiet roommate but we got along just fine despite my party moods at time. You learn to compromise a bit and most roommates go on to be friends for a long time after(big generalization there).
Bottom line: It's who you live with. If by chance issues arise the CA will be more than willing to help ya. Relax and enjoy the summer before uni starts. And gear up for Frosh week, It's amazing