Do you have a single servo running the elevator? If so when the halves were joined most likely the holes for the crossbar arrangement to join the elevator halves were not drilled in perfect alignment or there was too much slop in holes allowing one side to glue up slightly up or down from the other.

You maybe able to bend one side or the other to make the halves match. If that isn't possible open up one elevator half cutting the balsa where the connecting crossbar enters the elevator, free the metal and re-glue it in the proper position or alignment with the other half with epoxy.