Should I be concerned with a mole regrowing to previous size after punch biopsy?

Without a picture it is hard to say but it might not be the mole that regrew but rather a bumpy scar which is not uncommon.  If the original biopsy was benign then there should be no worry that the recurrent lesion is not benign.  If the recurrence is a scar, then having it re-excised might cause a worse scar.

Moles (nevi) that have been examined pathologically and deemed “benign” may still repopulate in the area of a biopsy months or years later. That does NOT mean that the mole is now cancerous, it’s just recurrent. Remember, it only takes a few nevus cells (melanocytes) left behind to entirely repopulate a mole. However, rapid growth, changing colors or symptoms do warrant a repeat biopsy. Small biopsies that are 1-2mm in diameter heal beautifully on the breast, larger ones can be a scarring challenge depending upon the tension of skin in that area.