Several things can go wrong
! Are the control horns mount EXACTLY the same on the elev.halves? Control holes must be even with the hinge line.
2 Are both serco shafts located to the rear or the front?
3 Most servo arms are marked to allow for correct spline location and centering. Check 'em.

Getting a dual control splitter with an adjustment pot for centering will most likely help cure most all if all the above is correct.
Above all don't give up... Find an Elmer ar someone to help. Most RC,ers love helping out new folks
Zebra
AMA129570