Hi and welcome!
If there's no way to incorporate the extra stitch into the pattern, don't do the increase. Since it's only a single stitch, it probably won't make a difference. Make sure that this stitch isn't compensating for a decrease toward the top of the leg. It may also help to read ahead to make sure that there's not something else intended for the extra stitch.
Adorable pattern. http://www.deramores.com/all-in-one-...cole-aran-3504