ROG
You said you practice a couple of times a week, but when it's match time, things seem to go downhill. I have to wonder what you are practicing, and how you go about it. Your practice time has to be time to build specific skills that will go with you when you compete.
You also need to develop a consistent, repeatable stroke that you can use on every shot.
The third important thing is to get your three routines perfected.
When you have these things firmly in your game through perfect practice routines, your mind is free from thinking about your fundamentals. Once you have done that, your mind is free to think about other things. Now, if you start thinking about all the people watching you, and whether you are playing up to their expectations (or your perception of what their expectations are), you can get in trouble.
If, on the other hand, you think only about the things you actually have control over (Angle, Speed, and Spin) you will find your game improving. Do your thinking about the shot at hand before you get down on your shot. Once you have made your decisions, get down on the shot and execute it. You have about 10 to 12 seconds before you will start second guessing yourself. That's where your routines come into play.
If you can get with a good instructor, as Ratta suggested, you can get the help you are looking for. If you don't know of a good instructor, let me know where you are, and I will see if I can offer some suggestions for you.
Steve