Tomorrow is my last treatment for yeast infection and I had sex today and when I whipped it was a little blood on the towel. Is that bad?

It is best to hold . Off on sex until you have completed treatment and your genitalia are no longer raw, red or swollen. If tissue is still raw, friction from vaginal intercourse could be reason for bleeding.
Likely not serious. Vaginal blood could be part of the yeast infection or start of menses. Follow up with your gyn for any concerns. Take care!