How to move an object along a spline ONLY on XY coords

Hello again!
I have the following system for moving my player. I thought it would help me move the player on the spline I was talking about in this thread. So I have the player spline right here (the green one):

Here is the blueprint for moving the player:

Unfortunately, I don’t think I can calibrate the torque so the player will stay on the spline, I think this is impossible. Could you give me some hints, please?