Rabbit breeding can be full of headaches. If a doe only conceives one or two kits, she will often go well over the normal 31 days' gestation. The kits wind up huge, and she has a lot of trouble giving birth to them. I have had to assist in several of these oversized kit deliveries. I've had a few does that I thought had done a false pregnancy deliver one huge kit about a week after their due date.
The crazy thing is, even if the doe does retain a kit, it isn't necessarily a disaster for the doe. Rabbits have an uncanny ability to wall off infection. Even with normal deliveries, it isn't unknown for a doe to not give birth to all of the kits inside her. Sometimes they just stop having effective contractions before all of the kits are out, and one or two don't get born with the others. Kits that get retained like this die, of course, and their bodies can get mummified inside the mother's uterus. A mummified kit can act like an IUD on that side of the doe's uterus, stopping the production of kits from that side. You can feel a mummy inside the doe. I have had a couple of does that passed a mummy during the process of birthing the (small) litter from the other horn - they are hard, almost snake-like in appearance, because there really isn't much to the skeleton of a kit, you know.
If you take your doe to a vet, the first thing they will do is examine her to see if they can feel a kit inside her. They may do an x-ray to see how many they can find. If the doe is in active labor, they may give her a shot of Oxytocin. Oxytocin is the hormone that causes contractions; it's what doctors give when they induce labor. I have known some experienced rabbit breeders who have managed to talk their Vets into letting them have a bottle of Oxytocin; it is normally only available to medical professionals (it can be dangerous if used incorrectly). A properly administered dose of Oxytocin produces hard contractions in an animal that is already laboring, so a litter will usually get born all at once, rather than being spaced out over maybe a half-hour.
Good luck, and keep us posted!