After you're done making sure the elevator halves are exactly the same run Peter Goldsmith's trimming sequence from the Model Aviation Feb and Apr issues in the Scale Aerobatics section. It is also posted here on RCU in a condensed version...just do a search for "Peter Goldsmith".

Basically you could also have a dynamic balancing issue (wingtip weight) even if your wings weigh the same, if the weight it distributed differently in each wing then under a load (pulling G's) your plane will pull to one side...or wingrock in a harrier/elevator.

Do the trimming, in order, you'll be happy you did!!!