i have so much compassion for you its unreal. I know what you are feeling because i think about my next BM before i have had one.
I hope i can help with some tips from your message and things you have said.
Learn to TRUST your body. I hear that you return to your dorm 'just in case' you need to go even if your body doesn't need to yet. That creates and expectation before your body is ready to go thus creating a vicious cycle of anxiety to poo to relieve your anxiety. What you need to do is go out and do what you want to do and dont let your body dictate to you that you must return to your dorm ready for relief. Trust that your body will produce what you want in the right time when no one is around. Don't trip your body into going home get some control back and you will find your angst will lessen.
Tell yourself to stop thinking about going to the toilet, your mind has got hold of the habit of thinking about it, just trust that in the morning your body will do the natural thing.
I have tried this and it works, if i don't go at all in the morning i put it down to my body not needing one today and i ignore that funny feeling in my tummy which i think is angst related. Then the next morning the poo is there!!!