Dear dmw13, Over the internet without being able to evaluate the scan, physical exam and question it is difficult to advise or to explain your doctors concern specifically for breast cancer. Lymph nodes can be enlarged for a number of reasons including cancer, and having this further evaluated is appropriate.
Very unlikely at age 29 unless you have a very strong family history of breast cancer with multiple first degree relatives. Still, it's one consideration out of many -- most of which are benign, like cat scratch disease if you have a cat, or just reactive nodes related to the car accident. I do think it is important to figure out why they are enlarged in case it is something serious that would require treatment. Finding out if it's both sides or just one will help narrow the possibilities.