This is what I think of as straight teen-girl YA. Molly thinks of herself as the "fat" girl who would rather have silent crushes than be outright crushed by rejection. She thinks everyone around her is much more experienced than her. She misses the clues that everyone else might just be faking it too. While Molly spends a lot of time thinking about her crushes, the real catalyst for the story is her twin sister becoming involved with her own love life and Molly feels left behind.
I've read reviews that knock this as "fat girl feels better when cute boy likes her" but I'd say that's a really narrow read of what happens with Molly. First, this is from Molly's perspective. She's the one calling herself "fat" but we don't actually know how the other characters interpret her. In fact, from what we are shown, it seems like people think Molly is an amazing DIYer, and good at conversation. She is the one who introduces her sister to the girl Molly thinks will be perfect for her. She is the one who has two boys quite interested in her. It's more what she chooses to believe. So I don't see this as the "fat girl being saved" but as the young girl realizing that not only is she not left behind, but the people who count, including her family, have been admiring her all along.
I would be surprised if there wasn't a high school girl out there who can't identify with Molly on some level, and that's Abertalli's specialty, taking the ordinary angst of being a teenager, and turning it into something affirming for her characters and her readers.