You MUST! take the other extra section out! Your liner was made to fit a specifically shaped pool and will not last long if installed in a pool that doesn't match it's specifications.

IMO- the wall foam is NOT as important as the liner fitting correctly!

Just make a vertical cut on the wallfoam (from top to bottom) and remove the extraneous panel. Then, overlap the foam, cut it on the overlap and remove the cut foam. Then, use duct tape to fully unite the two sections.

If you need more info from me, I'll answer.

(Thanks for the "heads-up" Lisa )