You said not to tell you to play more in front of people but that's exactly what you need !! One thing that you need anyway. Actually the same goes for your other topic about sight reading, do more sight reading.
You also should lose the concept that, what if a mistake should happen, because the simple truth is they do happen, even to the best players. At least so once in a while. The thing to work on of course is to practice to not make mistakes but more so, that when you do make one you can just play your way out of it. Don't let the mistake derail you. Later , after your performance, work on exactly why the mistake happened and learn then what you can do about it. You need to let a mistake during performance just kind of roll off your mind all together at that moment in time.
I knew a lady, relatively young woman with a couple of kids. She always showed up at the same work shops I attended ( I'm talking about decades ago here). She got up to perform her music at the work shop every month and just shook, her hands trembled. About three years into this it suddenly stopped and she played more advanced music too, the next year she was gone. I mean literally gone, she passed away from breast cancer. I believe the cancer was her bigger fear then and she no longer feared performance. She played beautifully. I can't interweave this story into anyone else's life but it just makes you think and wonder. I know that I've thought of it and her many times in my life since. I know that I've had my share of issues in front of a group of people and successes as well. What works for me is that I feel I have something to share with them and for the most part they enjoy hearing me play, so if there is a little slip up I don't worry about it anymore.
Edit:
Since Ian brought up about ignoring the audience, I will bring up another suggestion that I use. It's wonderful when you can get into that state of mind where it seems you just can't make a mistake, you just know that you will do this well, you simply have confidence and feel relaxed and it's like another power is taking you over ( sometimes I can feel a warmth take me over from within when and if this happens). Yes that is wonderful and it does happen but probably not day in and day out to much of anyone. So ignoring the crowd or ignoring that single person in the crowd that you know just bothers you sounds like a good idea. What helps me to get past that feeling is to play to someone in the crowd or even in a small group of people that you just absolutely know wants to hear you play ! If you think there isn't any single fan out there in the crowd ( but there probably is) then pick one or pick a guardian angel or something. Or for that matter just play to yourself ( some will say that's all in the same anyway). Seriously, ignore the crowd, ignore the critic in the crowd, play to a fan of yours even if it's your mom, play to an angel, play to yourself. In so doing the crowd and the critic in the crowd is ignored or it's effect is diminished at least.
All that said I'm working my way back myself, had been away from piano for a lot of years till a year ago May ! So I find myself working on these tricks myself, like I already did years ago.