You say you have to manually push the stern of the boat around.
As I mentioned early on, that tells me that you may be backing very deep into the water... It is a common error to back in so far that the boat floats over the bunks instead of settling in to them... Very often, a bunk trailer, when at the correct depth requires the boat to be winched the last few feet. If it drifts right up to the winch stand, you're in too deep... Another indicator of being in too deep is the stern floating up off of the trailer....
Also an even more common mistake when loading a boat is to sight from the helm, over the tip of the bow to the center of the tow vehicle. With the helm on the right side of the boat this will bring the boat in crooked every time... If you move your body to the center of the boat when lining up with the trailer OR sight off a spot on the bow ahead of the helm such as a cleat or part of a bow rail and line up with the right tail light you end up with a much better approach vector.
If after working on these you still have trouble you can affix tall guides to the back of the trailer.... There are multiple styles available but I prefer bunks, just below the rub rail and 3-4' long.... With them it becomes almost impossible to load the boat any way except perfect..
