Two of the most common reasons players don't play their best are overplaying and underplaying. Overplaying is when a player goes for shots that are beyond his level, such as trying to rip winners over and over rather than use more consistent opening attacks to set up easier winners (as well as winning a surprising number of points outright as opponents miss against your steady opening attack). Underplaying is the opposite - when a player plays too safe. Both of these often take place when a player is nervous. Under pressure, many players do one or the other, either getting wildly aggressive or too safe. The key is to find the right balance.
The way to develop a high-level attack isn't to rip every ball; it's to attack at the level you are consistent, and keep working to increase that level until you have a high-level attack. Way too many players want to rip that first ball when, if they'd take just a little off the shot, they'd be far more consistent and on the path to improvement. Top players may rip the ball harder on the first shot, but that's because they are farther along that road to improvement - they've put in the hours of developing that shot. So should you. So focus on making strong first attacks, and perhaps rip the next ball. A good general rule is this - until you have an easy pop-up, never attack at more than 80% speed.
The reverse are the players who have developed strong attacks, but are afraid to use them. If that's you, then the key is to simply learn to use those attack shots you've worked so hard to develop. If you can't do it in a tournament, perhaps work your way up to that. First use them in practice or league matches, especially against weaker players. Then against players your own level. When you can do that, then start using them in tournaments. If you have difficulty doing that, then the answer might be to play a series of tournaments in a row. That way you'll get used to playing tournament matches. You might only have to do this one time, i.e. find a series of weekends where you can play tournament after tournament, until you get used to it, and using the shots you do in practice becomes more natural to do in tournaments. Once you can do this one time, it's a habit you should be able to keep for a lifetime, at least as long as you practice enough to keep the shots in practice.
So a key to table tennis is that you not only have to develop your shots, you have to use them at the proper level, without over- or under-playing them, and keep developing your game so that this middle area gets better and better.