Do the easiest check first, lateral balance from the center point of the fuse fire wall. If its off, correct it then fly again to see the results. Usually planes pull to the left because(in hovers & verticals)of thrust, so adding right thrust helps. It could have too much right thrust and this can be checked by doing what was mentioned above, pull a straight up vertical with power on & take your hands off the sticks for a second, you will see which way it pulls.