Ironically, I had my first mammo last week, they just called to come in for more comprehensive scans. I'm sure it's nothing, but but it's always something isn't it?
Much easier said than done, but try not to worry. It is really common to have a call back, especially after your first mammogram (they have nothing to compare to, so anything the least bit unusual requires a call back). Due to a strong family history, I started mammograms at 25 years old and have had a slew of call backs. I tell myself that call backs are good - that means when I get a clean scan I can trust it, since they are so careful about calling back for anything remotely suspicious.