I would see if the LFS will take it back. If not see if you can find a buyer on here and post it for sale in the buy/sell livestock section. This is what some sites said they look like as adults
and this is what a different site said some breeding males will look like.
It will probably take a year before it starts growing fairly large and changing colouration a lot. However they are not reef safe. They will eat snails, crabs and shrimp and they will attack and possibly eat fish smaller then them. Basically as long as you have it you should not add any inverts, other wrasses, gobies, blennies, anthias, or dartfish to your tank as there is a good chance that your twin spot wrasse would kill them.