My appointment

So I went to the gynecologist and everything was fine except for they found a pea sized lump in my right breast so they want me to get an ultrasound which I have scheduled for the 13th. I’m just a little worried because cancer runs in the family like all types and me being me when they asked if I wanted the shot to help prevent some of the cancers I said do I have to have it and they said no so I didn’t get it was that a good idea or was that one of the biggest mistakes I will make in my life?