It is easy to check lateral ballance, and chances are if it is off, it will make a small difference, but right thrust is likely to be the culprit. It is especialy important when most of the air on the rudder is being spiraled back from the prop (not comming straight back from forward velocity). Another thing you could look at is, can you get more rudder throw? Once you get good at it, you don't absolutly need full throw, but being able to force the tail under the plane even when it has fallen out pretty far makes learning faster.