Continuity mistake: In the scene at the cove where Suzy and Sam are talking after swimming, the flower stem over Sam's ear keeps changing positions. In some shots it's parallel to the temple on his eyeglasses, and in others it's drooping down over his cheek.
Continuity mistake: Suzy flashes white panties while getting into the tent, but is wearing red check panties later.
Revealing mistake: When Sam first sets off in the canoe, it is obviously being towed because it leaves a moderate wake even though he is barely paddling.
Factual error: Suzy's bra is not typical of a young girl in 1965. Training bras in 1965, often manufactured by Teenform or Teencharm, were much more substantial and modest.
Other mistake: When the narrator holds up the wind speed gauge at the water's edge, strong whitecaps should have been visible to match the 22MPH indicated.