Video is wrong dimensions all of the sudden. Please help

I've been working on this video for a couple weeks and the format was fine, 16x9. Today I tried to transform one image to lay on top of the video and all of the sudden the entire project was in the long rectangle format. I tried to undo to see if there was some sort of step I had in there that messed it up but that didn't do anything.

Any advice would be appreciated! Thank you.