That's OK and it's at the bottom of the range for most efficient cycling. Typically this range starts with your heel on the pedal and legs straight (without rocking sideways) up to about 7-10mm above. The higher position tends to help faster spins and are used by track-racers. For most people, the heel on the pedal will be fine. Too low is more problematic than too high because it hinders spinning, promotes mashing and causes knee issues.