Agreed, all boats wander at slow speeds. It's a matter of physics. They don't wander loading on a trailer, unless you're lining up several hundred feet out. This sounds more like a simply oversteering issue. A boat won't react like a car. In a car, once you're pointed in the direction you want to go you straighten out the wheel. In a boat, when you do this the boat keeps turning well past your target point. Consider a boats slow reaction time. When you turn the wheel, the boat doesn't immediately start turning. Once it starts turning it doesn't immediately stop either. At slow speeds I try to think of it this way. If I want ot go to Stbd, I turn to stbd. Once the boat STARTS turning to Stbd, I straighten out. The boat ends up going well past where I straightend out and ends up where I wanted to go.
Also consider this phenomenon. When you steer a boat at slow speeds, you're not turning the bow, you're really turning the stern.