I'm in agreement with WashedOut - you really shouldn't over compensate with prescription drugs.
You might also find this link
interesting reading, it's one that I've posted before but could save you some money. Please read it to the end and you'll see missing three days is no problem at all
*I should probably add that I don't use Propecia and haven't personally tested the theory in the article. If you do decide to reduce the quantity/frequency of your dose you should make it a very slow transition.