I have had call backs for mamos. They did a compression/spot focal and a sonogram the first time. The second time the hospital had a new mamo machine and the spot focal was done then. Both times I had to have a biopsy. Everything was okay for me. Just remember that the new mamo machines can pick up a cancer the size of a grain of rice and smaller.
Just because you have a call back for more studies doesn't mean that it will be bad news. It means that they are making sure you are well. Please try not to worry, easier said than done, and let us know how things go.