Can try redo the whole process one more time as the photo merge sampling can left a spot here or there.

You may check each layer to see is if any of the layer mask giving problem or not.

Clone stamp (S) to sample the clean line (alt) and drag across by holding shift.Be certain horizon is perfectly straight.

Square marquee (M) the affected portion and (Shift+F5) to fill content aware.May take few tries as sampling of fill reacts differently every time.Clone stamp further if needed to make the fill blends with surrounding.

Square marquee a portion of clean horizon via layer cut (M,Carl J) and free transform (CtrlT) across the affected area.This work best again on straight horizon.

Different people have different approach.Just try la!

This post has been edited by 6so: Jan 4 2014, 11:05 PM