You can sort of do that with ProTan. It's actually meant to tan you semi-permanently, but it goes on much darker than the tan it leaves behind once washed away. So you could in theory use it in a temporary fashion by applying just one coat and leaving it on for the competition. While the pro-tan is on, you'll be about 5 shades darker than your normal color, but after you wash it away, you'll be only one shade darker. That way it won't be nearly as noticeable at school the following Monday.

Other than that, the only truly temporary solution I know of is called "makeup". There is such a thing as body makeup, if you have a more revealing outfit. If you're really concerned about your appearance at school, you may just want to consider wearing less revealing Latin outfits for now. That way there's less to tan.

Sincerely,
Jonathan