Try not to fret too much. The majority of referrals to a dermatologist and subsequent excisions for biopsies turn out to be benign, but in these circumstances it is always good to get it checked. 

Unfortunately my wife's growth turned out to be malignant, even so, she had it removed together with a wide excision and lymph node biopsy, this all came back clear. She has 3 monthly skin checks for the  next 5 years to check for any recurrance, the chances are that when its caught relatively early and hasnt spread to the lymph nodes, she will not have a recurrence. 

Moles and melanoma can be unpredictable, dermatologists cant always tell by looking at it, hence why they may refer you for a biopsy.  Treatments for melanoma have come on leaps and bounds over the last few years, hopefully yours turns out to be benign try to not let it rule you before your appointment. 

Best wishes to you for your up coming appointment.