Until you realize YOU are responsible for all of the thoughts in your head (positive and negative) you will always have issues with confidence and nerves. You create fear by the way you talk to yourself in your mind. You can also created confidence. Stop playing scares. Start getting excited.
Never stop giving your best until the match is over. Focus on playing smart (being in the right position / making the right decision). And don't be afraid to use those skills you've been working so hard to improve.