First of all, I'm not familiar with the plane. There may be some differential deflection already built in to the controls. This is unlikely though.

When you say there is more travel, do you mean the servo arm or the pushrod?

If it's the servo, be sure you don't have any subtrim in your radio. Also check your other computer settings just in case.

If the servo has the same amount of throw both directions, check to make sure the point where your pushrod connects with the control horn is exactly over the hinge line.

-Andrew