Projecting to the xy plane

Hi, I have a (hopefully) simple question:

I’ve drawn a floorplan that looks fine when I am viewing from the “top” view, but it turns out that it is not all drawn on the xy plane. Therefore, I can’t trim lines because the lines are floating on top of one another in the z plane. Is there some quick way to project everything to the xy plane? I’ve tried make2d but it doesn’t seem to work for me.

In top view select all and 'project to cplane’