Of course not! A nodule, density or lump in the breast is very common and most are benign. Also to be called back for further investigation is not unusual at all. The Mammogram you’ll be having is a type of mammogram (spot compression) in which only a small area of the breast is compressed that will further define the area of concern and help to clarify. Sometimes the tissue can fold over on itself and cause a "density" to appear. A spot compression will smooth out the tissue and the "density" will disappear. Often, a second mammogram will confirm that all is okay and the Ultrasound won’t be even necessary, unless the density is still there after the diagnostic Mammogram .
I hope that all will be just fine with your upcoming tests.