I Have Been Told By My Doctor That The Sore

I have been told by my doctor that the sore on the roof of my mouth is just a blood blister. I have had it about 7 months. It does not hurt but I can feel it when I take my false test out. Should I be concerned or will it eventually go away on it's own? My dentist said it looked like an adult pimple to him and wasn't' too concerned either because it did not look like cancer. What would cause it as my false teeth are fitting okay?