I'm 31 i just had my first mammo/us. the dr says my left lymphnode under my left arm looks a lil wierd in color size is good may need bx. cancer?

Listen to your Docto: I guess your doctor is concerned and for your own safety it's better to listen to his advice. No one is immune to cancer , even though statistically the probability is low. As they say " better safe than sorry".

Most of the time: it turns out to be a benign reactive lymph node. However, I don't know your full clinical picture, and if it is suspicious enough to warrant a biopsy, there is at least some small probability that it could, unfortunately, be malignant. Best bet is to talk to your doctor about his/her level of suspicion.