Dear mercedes622: It is not uncommon to do an ultrasound to explore an area that may need further investigation after a mammogram. Ultrasound it is a better test to determine whether a density is solid or cystic (fluid filled).
An ultrasound is no big deal. Earlier detection means better everything. Chances are very good that there is nothing to worry about. Don't worry - go ahead with it!
An ultrasound isn't going to hurt you. Why wouldn't you want to know what's going on with your body? Dense breasts are more difficult to read but also present a higher risk because of that. You have the right to say no to any treatment. As a survivor, I'm going to tell you to do this ultrasound. You want records for them to use when you go again next year to see if there are any subtle changes ... or not so subtle changes. Don't let your fear override good common sense. Best wishes.