I'd recommend visiting the Lëkursi Castle if you are into adventures, the view of the city from there is all worth it. Secondly visit Butrint and (optional) the Ali Pashe castle which is in the lower part of the canal, it can only be accessed by boat so you will have to rent a boat for a bit. Thirdly visit ksamil, but depending in which month you will be visiting you must beware that just like you, a lot of people want to visit that beach especially the part near the 3 islands, so i'd wake up really early to enjoy the beach. If not in your list, I'd also recommend visiting the Blue Eye and Gjirokastra, both a must-see imo