Had a large blister on the bottom of my foot and popped it. it now has a red ring around it, the skin is really hard. it is itchy. is it infected?

Please see: Please see your dermatologist for evaluation and to discuss treatment options. This way you can get the best treatment.

Possible: It's possibly infected with fungus or yeast. It's probably not a bacterial infection from your description. Apply topical lortisome (antifungal cream with hydrocortisone) and bandaid for one week. If skin feels worse or appears like its spreading, see a doctor. Hope that helps.