Getting another is the safest thing to do. Sitting at full charg for that long, the internal resistance has increased and it'll no longer be like it was before even if it doesn't continue to swell. Its damaged and the swelling is just part of that damage.

You can try to cycle it and see if it goes down, but watch it carefully and make sure its not increasing in size at any stage. It it does, immed stop and remove it to somewhere it can't do any damage if it vents.

I'd get another personally.