Sand reflects light, yes. For ISO100, f/22 @125 will give you the correct exposure with blue sky. You won't need 1/500 unless you open the aperture to f/11. If you're wanting to use wide apertures at the beach, a point-and-shoot is almost certainly the wrong tool. :P

I don't know if anyone has mentioned pulling your film yet. Pulling is overexpose/underdevelop, the opposite of a push. Tames contrast, increases tonal resolution.

Tri-X looks very nice at EI 200 in bright light.