Other mistake: Sammy makes his film "Escape to Nowhere" with a Bolex 16mm camera. (I recognise it because I own one.) When he shows the film, we can see that it is on 8mm film.
Continuity mistake: When Sammy is learning his lifesaver lessons, he leans on the edge of the counter. From the opposite angle, his hand has moved several inches to the centre.
Mitzi Fabelman: Everything happens for a reason.