The fact that you already realize that you're inner game is weak, makes a solution much easier. You want to change, which I can only encourage you to do.
Possibly the best way to fix your inner game, is by working on your outer game. It's like a vicious circle: Improving your outer game, will get you some results, which will fix your inner game, which will get you even better results, which will fix your inner game even more etc etc...
Some things that might help:
Try noticing every day how people like you: Women making eyecontact, you having fun with your friends etc.
RSD focuses very much on inner game (having fun instead of knowing techniques), read some of their material.
Simple exercise for starters: Start believing that your game is a 10, on a scale from 1 to 10. Nothing more, nothing less.
Take the positivity challenge:
http://www.positivityblog.com/index.php ... challenge/
Good luck!