HELP ME FIND THIS BOOK! a physical, two-in-one novel where the book features two front covers and two separate stories.

hey, so I’ve been searching for this book for years. I remember reading it when I was maybe 14 that was in like 2017. It was like a book and I think this girls mom worked in a lighthouse, but I’m also not sure. I think her parents could be wrong, but I remember her riding her bike around the town a lot and I remember they’re being this older man who everyone in the town thought was but this girl meets this boy her age and they get along a boat making contest. I think it was and it turns out that that old man is his and he’s not so bad he’s just not really a people person but I remember them building the boat or something in his grandfather‘s backyard and they like take a break and go in the woods and eat a sandwich by the water or something and I think that’s all I remember but please help me find this book and I’m not sure what the other book was on the other side like I said it was a so if you turn the book around and turn it upside down, it was a different story completely different but I don’t remember what it was