You didn't give enough info to fully describe you situation. Is you hull a
flat boat ( jon boat) or does it have a pointed bow and some forward vee?
Without knowing anymore I could only say that maybe you are backing your
trailer in too deep and the boat is floating around over the bunks and when
you pull out the boat settles where ever until you get lucky and have is
cone to rest in center on your third try? Anyway if this seem plausible,
then try to load your boat while it has some contact with the bunks, ( don't
back in so deep).

--
Ron White
Boat building web address is
www.concentric.net/~knotreel