I have never been to prison thankfully, but I can relate to you with regards to feeling institionalized, as about five years ago I spent 15 months in psychiatric hospital only to spend a further 9 months a couple of months after being released. The main feeling I felt was anger at having lost a significant period of my life when I hadn't even done anything wrong or illegal. I still feel a little bitter even today. I found it difficult to adapt to normal life for a while but after I had been out for a month or so I found it much easier to cope and adjust. Just think to yourself that life in prison is such a waste of your precious time on this earth and try and be thankful that you're out, despite how difficult it may seem. Give it time and eventually you will find it easier, but you must try your hardest to stay out of trouble since it's just not worth it.
You really should try and integrate into society as best you can, making friends and relying on some sort of support network like your family if that's possible. I think that would really help to keep you on the straight and narrow and it's just good for your mental wellbeing to have a healthy social life with good friends that won't get you into trouble after such a difficult experience. I would recommend finding a hobby as well, since that really does help to take your mind off things. Things will get easier, trust me.
It does sound like you're adjusting well, so I really wouldn't worry to much about being institutionalized.