Scott,

It seems you're taking the hard way to make a textured floor.

SH3D is designed to make this porcess real easy, as follows:
1 - draw your walls (and make sure end wall and start wall are locked or overlapping);
2 - double-click inside the walls to create a room;
3 - right-click the room and apply a texture (works the same for walls and rooms);
4 - if you don't have the right texture, click on Import and select the correct image;

This is described in detail in the User's guide. Maybe you haven't taken the time to read it?

Hans