Ack. Yes you’re quite right to be worried. I know there are certain ways to properly care for a wild baby rabbit I personally do not know them myself. I know it involves hand feeding quite often. The best chances of survival is handing the baby bunny over to a wildlife rehabilitation center because they will know the best ways to take care of the animal. You can phone local shelters and pet stores to find these centers and get in touch with them.
The proper thing to do when finding a lone bunny if he/she’s not in any sort of immediate danger is to leave he/she where you’ve found them. Just because the bunny is alone doesn’t mean their mother isn’t around somewhere. If the bunny is touched it’s best to have the least amount of contact with humans as possible leave them where you found them and wait a day or two to see if the mother has come and picked him/her up yet.
Best of luck, hope everything turns out alright! <3