You can buy a fake tan remover at the chemist and the supermarket but it would be a pretty massive job to do your legs. I think it's more to get rid of little mistakes - I wash my hands with it after I tan so my nails don't get stained.
I would either go back and get them to fix it, or do you can any bronzer or shimmer that you can mix in with moisturiser? It will give your legs a glossy sheen (makes you sound like a racehorse )and the colour should look a little more even.