Seems to be a common problem...
How does it sit on the trailer? Looking down the trailer from the tongue, is it sitting dead center but crooked clockwise or counter clockwise, or is it shifted from the centerline of the trailer?If the problem is the former, it's simply that you have too much weight on one side of the boat. This causes it to sit in the water listing to one side, and when you pull it out thats the way it rests on the trailer. Even out the stuff you have stored in it so that it sits level in the water.If its the latter, it's just not centered over the trailer when you pull it out. Theres a number of things you can do. For now, if you have someone with you, have them hold the boat in the right position and walk along the dock as you pull it out. Better yet, do it yourself, and have them pull the boat out.A more permanent solution would be to set up some sort of guidence system to keep your boat aligned. Many people use a piece of electrical conduit with one of pvc slipped over it. This allows the PVC to roll and won't mar the boat as it slides through them. If you go the the launch on a busy day, you can easily find a trailer with these on it.A larger sailboat might require two sets of these, one near the rear of the trailer and maybe one forward of the centerline.I have also seen a PVC guidence system set up for the keel (Credit to David Clark and his 222!). This works the same as above, but is more likely to even out any gentle listing your boat might be suffering.Hope that helps, if you have any more information or some pictures, Im sure myself or others can give you more info if you need it!Josh