It sounds like you have had to find courage to take this step and I hope that ultimately it is helpful to you. I don't have personal experience attending an IOP, but I think some general ideas about encountering new things could be good to focus on. For example, try to understand everything you can about the program now so that you have an idea of what to expect.
Maybe you can get familiar with the route there by actually practicing going there or using something like Google maps to get familiar with what the place looks like. When I started a new job a year and a half ago, I made sure to travel to the location two times before my first day of work. This gave me more peace on my first day because I was already familiar with how to get there.
Between now, and then, try to keep your mind occupied with things other than the worries that you have. Of course, it's good to recognize your worries and process them, but sometimes when there is a long time to wait for something, our imaginations can run away with negative thinking. Try to focus on any hope that you have for the program and not focus too much on the unknown.
Will be wishing you great luck and success.