Question about Mammogram Findings

Thank you for taking the time to answer my questions.  I am 35 years old, no breast cancer history in family.  Went for first baseline mammogram.  Received a call to come back for another mammogram and ultrasound.  On the report the findings are:  The parenchyma is heterogeneously dense. Asymmetries are seen in the inferior left breast and the upper outer right breast, for which additional spot compression and bilateral ultrasound is recommended. Conclusion : Bilateral asymmetries, for which additional evaluation is recommended.  BIRADS: 0- Incomplete, needs additional imaging.  
I understand the BIRADS, and understand that further imaging is necessary, however what does the rest of this mean?  Is this anything to be concerned about, or just means they want better views?  I did make my next appointment, and go next week.  I would just like an opinion on what this means?
Thank you very much for your time.  

[Cleveland Clinic]

Dear  AMC5: It is not uncommon for a density to show up on a screening mammogram.  When this happens, the radiologist will typically call the woman to come back for further evaluation such as a spot compression where a more specific view of the abnormality can be obtained.  In many cases, the density could be as simple as some tissue that has folded over on itself and will resolve with compression.  However, the spot compression will take a closer look and help to determine if there is an abnormality and whether any additional evaluation is necessary.