The fawn isn’t abandoned and you should leave it right where it is.
There is a strong probability that you did not find an abandoned fawn. Female deer hide their newborn fawns in tall grass or brush and move some distance away to feed to avoid drawing predators to their offspring. With the proliferation of deer in suburban areas, sometimes this happens right in our own yards. The fawn simply waits in hiding until its mother returns. Soon, the fawns will be strong enough to follow the does and run from predators, and they no longer need to spend hours alone in hiding.