Is my Accutane dosage accurate @ 20mg twice a day? Side effects are only excessively dry lips and noticeably thinner hair.

I think you should be on 0.5 - 1 mg/kg per day for at least 20 weeks.  However, efficacy is really based on the cumulative dose, so if you take half the recommended dosage, then you should be on it for at least 40 weeks.  Sometimes dosage is kept low because of side effects, so if you don't want potentially drier lips or more thinning hair, you may want to stay on this lower dose for a longer period of time.

You don't have to suffer bad side effects for Accutane to be effective. Seeing as I have prescribed Accutane for about 30 years, I rarely have to ask a patient's weight and can get within about 5 lbs with just a guess. My assumption is your doctor did the same thing. Starting a patient at 20mg BID is quite normal. And I wouldn't up your dosage. "This answer has been solicited without seeing this patient and
cannot be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."