Other mistake: If Madison can't swim then how is she going in the water, up to her shoulders, towards Ben prior to them having sex?
Suggested correction: She trusts Ben will not let her drown and holds on to him, keeping her up.
No if you watch she's several feet in there away from him and the ladder behind her and this is the deep end of the pool.
Character mistake: When Ben and Amy are in the diner discussing their college plans and getting an apartment, Ben calls her "Annie" instead of "Amy." (00:10:10)
Suggested correction: He says "Amy. Amy." He says it quickly though because he's trying to stop her train of thought since he hasn't even been accepted into college yet.