How do I fix my prototype of my Level Maker?

I'm making a Level maker in my Game, but for some reason, the prototype won't work.

Here is a few second video of everything I think you need to know to help me fix this.

drive.google.com/file/d/0Bw7SYAAkapF1bXN3dEhpVklWdGM/view

(Also, I'm using a Tilemap)

If you need more information, just ask me.

The mouse position doesn't translate 1 to 1 to the tile position. If the mouse is at X 200, that translates to 200 tiles to the right

There's information about that in the manual