You are not stupid for getting a mammo at 42, but very smart! Good for you!
Unfortunately, the answer is yes, some people are prone to cancer with genetic predispositions. Having a BRCA 1 or BRCA2 mutation can place you at higher risk for certain cancers, including breast, colon, prostate (men) and ovarian. If you have one of the genetic mutations from the BRCA gene, you probably have other family members with a history of these cancers especially at a young age.
However, many of us believe that the absence of a genetic marker does not automatically mean there is none, just means that there is probably one that has not yet been discovered.
With your history, if it were me, I would stay under close surveillance with the medical team, don't let them ignore you and consider seeing a genetic counselor at a cancer center to discuss your options.
And tough as it is, try not to worry too much about
the mammogram just yet...there are so many people who have to have multiple views taken just to get a better read on something. Very good chance that there is nothing, but worrying won't change the outcome. Advocate for yourself and don't stop till you are satisfied with the replies and the care.