It is very common to see a spotted fawn instinctively lying very still and flat by itself with no adult nearby so as to not attract predators. Female deer leave their babies unattended for long periods of time while foraging for food and return only to briefly nurse the baby. The mother deer is usually in the area observing from a distance.
There are a few tests that you can do that will help determine if the baby TRULY needs help: (It is OK to touch the baby while doing these tests).
If the fawn passes all the tests LEAVE IT ALONE! Mom is nearby and taking care of her baby. If the fawn fails any of the tests, it MAY need help.
DO NOT ATTEMPT TO THE FEED THE BABY.