The final shot of the twins' wet birthday cake (soaked by Toast's 'cannonball' into the swimming pool) is flopped: not only is the model Ford Mustang on top facing in the opposite direction than before, but the lettering on the "SWEET 16" banner is in reverse.
After Kylie discovers that Taylor, Lyndi, and Danny are not on the bus, they are, in a later scene, shown walking toward the front of the bus, with all their luggage, and they are presumably getting off. When the story later goes back to Kylie and the other three, the bus is driving up to a bus stop and they get off the bus. They should have already been off the bus, considering they would not be standing while the bus was still moving, and there was no-one else on the bus in the previous scene.
Ashley's/Taylor's hair colour changes throughout the film. At the beginning, her hair is quite blonde, but when she arrives in Bishop, her hair clearly has had more brown put in, but nearer the end, it lightens again.