I got diagnosed when I was 18 and just started studying at university. I had quite some problems during that time leading to surgery when I was 22. By that time I had graduated already (got my first degree quite quickly at 21).
In any event, in retrospect, if I had been treated properly back at university, did enough sport and generally had been a calmer person, things would have been better.
My tips would be to run your Crohn's management very well during your time at university and be rather strict about it. That might impact your social life (as in drinking heavily and partying all night eating junk food is a big no-no, at least it is for me), but doesn't mean your social life has to ceize. Quite on the contrary, you just need to adhere to some guidelines, even if those guidelines seem restrictive at first.
Re exams, my Crohn's never bothered me during exams. However, it you have problems and you are preparing for exams, it can be quite hard to prepare sufficiently. I can just reiterate that managing your Crohn's right is also the key to not getting into troubles with exams or exam prep schedules. On the anxiety part, the only thing that ever helped me is enough preparation AND the knowledge that I was quite good at university, so nothing much could happen.