Ongoing Accutane. I finished my 4th course of Accutane at the beginning of Dec & this week a couple of whiteheads have appeared

My dermatologist said that after my 6 month course, we could try 20mg a day on an ongoing basis to keep my acne under control . My questions are: 1)If i begin 20mg over a month after I finished my course, do you think that it will be sufficient enough to keep it under control or did I miss that boat when I didn't immediately drop to 20mg a day 2)Do you think 20mg on an ongoing basis would do harm? My liver results have always come back fine.