What is this on my dog ?

Hello Vets and Thank you in advance !  Several days ago , I notices 4 spots on my dogs stomach.  3 are very tiny , and the largest is the size of a nickel .  Originally it looked crusty, and I bought both a shampoo and spray that is both antibacterial and antifungal . Ive used it for two days , and when I used it , the crust dissolved and this is what the  spot looks like .    Does this look like ringworm to you ?  If he doesn't clear up in a few days after using the shampoo and spray I will take him to his Vet.  I don't know where he would have came into contact with anything . He is an indoor dog.  Only goes out to potty . Any thoughts are greatly appreciated .