Do I have a double chin? I am a pretty active, average weight 20 year old woman. (Photo)

Double chin is secondary to excess of fat in the neck under the chin and under the jaw line.
Chin liposuction is the plastic surgery procedure that removes the excess of skin of the neck thus correcting the double chin. Also when performed along the jaw line it helps to achieve a very sharp jaw line. In female patients chin liposuction when performed also along the jaw line helps to achieve a very chiseled sharp and more attractive feminine facial look. In my practice I often perform chin liposuction wide awake under local anesthesia as an outpatient at my office operating room. 

Hello and thank-you for sharing your question and photo.
Correction of a double chin can be achieved either though a surgical or non-invasive approaches. Liposuction and Jplazty (cold plasma energy to tighten skin) of the chin and neck produces consistently good results for appropriate candidates.  We are very excited with the development of several non-invasive techniques for correction of a double chin. Ultherapy of the lower face and  submental neck can provide both skin tightening and fat reduction for more definition.  We also offer the Cool mini as a non-surgical alternative to liposuction for the right candidate. Generally, two treatments are required separated by 4-6 weeks.  We also offer Kybella which is another non-surgical alternative to liposuction. Generally 3-6 treatments are needed separated by 4-6 weeks.   
I would discuss your goals and expectations with your surgeon. 
Good Luck!

You appear to have some fat under the jawline. Neck liposuction is a great option for patients with good skin elasticity and excess fat in the neck and around the jawline. Liposuction is effective at removing this excess fat and stimulating the skin to contract over time to create improved angulation and definition along the jawline. I recommend seeing an expert for a consultation. I hope this helps!