Have you ever had to cancel a stay once it began? What happened?

I just recently signed up to board on Rover and I'm afraid I may have gotten in over my head. My dog has been much less receptive than I thought he would be to the situation. I'm currently monitoring all interactions between my dog and the one I am boarding, but any time the one I'm boarding trys to interact with my dog, my dog becomes still and then very aggressively growls and occasionally lunges at the other dog. I am doing everything I can to try and get them to get along and I understand this may take a day or two to smooth over. My condo is relatively small which is fine since the dog I'm watching is also very small, but it makes separation of my dog and the other dog not possible. If I ultimately think the dog I'm boarding's safety is a concern I have been assured by Rover that arrangements for a new sitter to take over is an option, but I want to do everything I can to avoid that..

My question is, have you dealt with this situation, and how did you deal with it? I've never had problems with my dog being territorial or aggressive in the past and I have had experience with high anxiety dogs in the past, but in situations where I could more easily separate the animals. I know this is unprofessional and it's honestly embarrassing but I'm afraid I may have gotten in over my head with this. One thing is for sure, I will only be offering dog sitting at the owners house and walks/visits in the future if I were to keep doing this at all, which I am reconsidering. I think boarding in the future will be too stressful for my dog and possibly endanger the owner's dog.