The short answer is no.
Every ranked round you play will affect your "average" until you saturate (or hit the required number of rounds for that tier - I think it is 50 at TM), thereafter it will only drop as the highest scores drop of the computation.
But there is no turning back I am afraid, you can only look in the rear vision mirror.
Just have fun, read the forums for help and learn - like riding a bike, you will pick it up pretty quickly again.