I have an anal fissure and was prescribed a nifedipine ointment. Will using more often/more than a pea-sized drop do me harm?

No. The nifepinine works by relaxing the rectal muscles. There is a limited rate that it can diffuse through the rectal lining into the muscles. Putting more cream on may not increase how well it works but shouldn't harm you. Realize that it is not a pain reliever or an anti-infamitory so relief will take time. Don't over do it because that just irritate things. Good health.
Use as directed. Use medications as directed only. Do not use more than directed by your doctor.
Maybe,maybe not . The dose you listed is considered more than adequate for the medication to work. Both 2 and 3 x daily dosing has been suggested in references. A variety of side effects including dizziness, nausea, light headedness, pallor and heart rate changes are occasionally seen and may be more likely with a larger dose.Larger doses will not necessarily speed healing.