I totally know what you are going through. I had to rush my rotti to the vet the morning of one of my finals when I was in college. I arrived to the vet in tears and left in tears. Then had to drive straight to my final exam from the vets office, leaving my poor, sick doggie behind. Fortunately the vet was close and school was close too, and my father and brother stayed behind with my dog. I had to just get myself together and take that exam.
Now comes the hard part. If you have absolutely no way to get your bunny to the rabbit vet, and if your current vet office can't help you out by maybe watching him while you are at school? Here's what you're left with:
1. Finish that paper
2. Take that exam
If your professors are anything like mine were they're not going to take a late paper, and they're not going to let you take that exam late either.
Just do what you can for your bunny while you are still there, and maybe leave him with plenty to eat while you are gone. It might help if you got as much as you could into his belly between now and then. You can't beat yourself up right now. This is the eleventh hour. Good luck. Prayers and hugs out to you!