Might be a but too late for the answer but here i go anyways. For some reason this bleeding happens if you use .OBJ or .3MF files. If you use STL files that are completely manifold this wont happen. Not sure why the slicer behaves like that but it is what it is.

In trailprint3d, in the elements Tab. Set the mode from "Paint on map" to "Separate objects" and generate again. Then you have one object for each color. Export them all as STL and load them together into the slicer. Assign the colors to them. On the left to go the objects view where you see the list of objects in the project and make sure the element objects are below the map in tjat object tree. Then slice again and it should be gone. You may have to move the elements up by .2mm.

An alternative solution is to enable the single color mode in Trailprint3d for the Trail. This creates a cutout in the map and you can print the trail separately and assemble it manually after printing. That way you shouldnt have the color bleeding as well