I understand, but try not to worry about something that may never happen. This is all very new to you. It's very common to feel particularly scared when you first experience symptoms or get given a diagnosis like IBD. It takes time to get your head round it. At the moment it's still a shock to you. Give yourself some time, a few more weeks maybe, and you may start to find your life going back to normal again, not necessarily because your symptoms go away or because you get a clear diagnosis or because Crohn's gets ruled out through further testing, but because living with the knowledge that you have IBD becomes more familiar. You'll probably learn quite a bit more about it, and won't feel the fear that comes from facing the unknown. Many people here have gone through a similar process of mental adjustment.
That said, if the biopsies showed no sign of Crohn's, that's more significant than the doctor's suggestion that you may have Crohn's - and it sounds like the doctor feels that way about it too, since he said the biopsies would allow him to know more. Biopsies provide better information than what the doctor sees when doing a scope. So "transient colitis" is your diagnosis at present, which means temporary inflammation of the colon. It's a vague diagnosis as it doesn't specify the type of inflammation, but I think at the moment there's little reason to worry you may develop severe Crohn's disease - even when the doctor thought the inflammation looked like Crohn's he said it was mild.
At the moment it doesn't seem like there's much reason to worry that you may go on to develop severe Crohn's. Another appointment to discuss this with your doctor may help you. Even if this isn't just a temporary condition and you do develop symptoms again, don't panic; just report them to your doctor. IBD is treatable, you will manage. For now, enjoy being symptom-free.