Try not to freak yourself out too much! I have been in your boat and had the results go both ways before. The dog I just adopted a month or so ago had a huge lump on his leg and I was talking to my vet friend before it got tested and she said due to the location of his lump and how fast it grew to prepare for the worst. Well the results came back and it was just a harmless cyst. I was in tears fearing the worst when I should have just enjoyed my time with him no matter what until the results came ( I know that is really hard)
The other dog that indeed it did turn out to be cancer, I lost precious time with him already mourning him being gone before the results came back and I regret that because he knew I was upset and it made him upset.
Also, from what I understand from your post if its a small spot that has hardly grown on top of the skin that seems to be something that could be removed way easier than a huge tumor in a terrible location.
Another thing to add, with my dog who did have cancer. His appetite changed, he became lethargic, he lost weight and was slowly no longer my happy little guy.
They are probably going to remove the whole thing and send it off to the lab and that is why he would need surgery rather than a fine needle aspirate since as a scab there is likely no fluid for the vet to pull out like there would be for a tumor.
I'm hoping for the best for you! I know it is so hard to deal with and I'm sending good thoughts your way! I hope it's harmless and your pup is fine