I contacted AO3 Support and they replied with the following:

"It looks like your work is added to two collections. The collection "Space_Swap" is still anonymous.

To take your work out of the collection:

1) Log in.
2) Edit your work.
3) Scroll down to the Associations section, find the collection name next to the Post to Collections / Challenges option, and click the red ‘X’ next to the name.
4) Post without preview."

It worked perfectly, in case anyone else is having the same problems.