You didn’t make the wrong choice by selecting Osgoode. I absolutely loved my time there and I think you will too. The beauty about going to a larger school is that you’re bound to find a group of people you click with - even if they aren’t in your section. I found 95% of the people there to be very collegial. No one is going to be ripping pages out of books or trying to sabotage you.
I won’t sugar coat it - 1L is stressful. Being graded on a curve against other highly capable students is stressful. Learning a new subject area is stressful. The pressure to get a “summer job” will be stressful. These things are not exclusive to osgoode and the stress won’t be exclusive to you. Everyone will be going through it at the same time and you’ll find people you can lean on. The upper years will be a particularly valuable resource for helping you manage your stress.
There is no point in fretting about September (August in your case). It’s will be a bit stressful but certainly nothing you can’t handle.