Try to export as a cropped gif

So, I recorded something that I wanted to make a gif out of. I trimmed it down in shotcut, then tried to export as a gif. It worked, except it exported in 16:9 and there are these black bars on either side of the animation. I tried changing the aspect ratio to something like 4:3, but that just made black bars appear all around it. What am I missing?

That helped a lot! Making a custom project resolution worked. Thank you!