It sounds like you have the right mindset! I was only in for 30 days and the first couple of weeks were very hard for the reasons you described. After I adjusted to the schedule I started to make connections to the people there. I really started to get into the flow of it the last week or so. I hope to never go again, but I'm so glad I did. In retrospect, I think I would have liked to stay or 90 though, but I couldn't afford it at the time.
Best advice I have is to try to get into the flow of the place and don't fight it. Try to make friends with people there and find people you can talk to/hang out with. I don't know if there is a blackout period for your treatment center, but the one that I went to didn't allow you to talk to anyone from the outside for the first week, and that was a lot harder than I thought it would be.
Try to bring books! After the first week the first thing I did was call my parents and tell them to bring as many books as they could carry. I'm not much of a TV watcher, so I spent a lot of time reading.
Try to enjoy yourself! It's going to be your time to really focus on your mental health. When I look back, I really almost think of that time like it was a vacation -- a chance to call a "time out" on life and sort out a lot of crap.
Best wishes to you, I hope you learn a lot.