Fur loss and dandruff along the back, will often indicate fur mites. There are other possible causes, like sebaceous adenitis, but the other causes are less common. Treatment for fur mites will usually be three injections of ivermectin two weeks apart, or one spot on application of Revolution(selamectin) will usually be enough to clear up the mites. If it is fur mites and you have a choice of which antiparasitic is used, I would ask for the single application of Revolution. It's easier and a little bit safer over the ivermectin. Some rabbits can be more sensitive to the ivermectin.
It doesn't look too bad at this point, so you're probably fine until the vet appointment next week. But if you notice any worsening of condition that causes you concern, or your rabbit stops eating, then phone the vet to get your bun seen sooner as an emergency if possible.
https://wabbitwiki.com/wiki/Mites
Medirabbit: fur mites