Determining if a fawn is an orphan, learn more here.
The chances are if you found a baby fawn, it is probably doing just fine on its own. The parents leave fawns alone on the average for six hours. It is natural to think that if you see a fawn left alone for an extended period of time that it needs help. While the parents are out looking for food, fawns are very well camouflaged, will lay perfectly still while waiting, and have almost no scent that the predators can detect.
Some good signs to determine if a fawn needs help is if it is laying next to an injured or deceased parent, its front legs are splayed out, if it is limping, has swelling around the eyes, is constantly calling out is covered with ticks, in which case, you should call The Wildlife Center of Southwest Florida. Otherwise, it is probably doing fine.
As always, it is best not to try to feed it or keep it as a pet. Young fawns are very hard to raise, can pack a pretty solid kick, and are best not getting imprinted (getting used to human contact).