Selecting Drawings

I'm brand new to Roll20 and I'm trying to transpose a physical map using the VTT. I used a polygon to make the walls, but have a square (unattached to the base polygon) I want to delete. I can't select the square. Clicking doesn't work. Clicking and dragging selects both the square and the base polygon. I'm sure I'm missing something, but select and delete just isn't working, since it selects both drawings.

Click dragging across just one of the elements should work, but is it possible that the drawings are grouped? After selecting, right click and go to advanced, then click ungroup and try again.

You can also try zooming in as far as you can on a segment of the square (making the line appear a little thicker on screen) and see if you can click to select it there and then delete it. And if you accidentally delete your other polygon, be sure to hit Ctrl-Z right away to undo.

Thanks for the replies. I just was able to make it work somehow after logging back in. I don't know what the problem was, so I'll just have to watch for it happening again.