Blisters are the weakest link and thus the biggest risk when Vacuum Hanging.
This is why proper set-up with positive Glans-Lock is critical. It is also vitally important to take your time to learn the proper set-up and gain the experience required to know the optimum conditions for maximum intensity without over doing it.
The suggested beginners 3-month template is very conservative with 8 lbs targeted after three months with a regular ie. consistent routine.
Blisters can be avoided when you recognize the tell tale tingling/stinging sensation that indicates a blister is potentially forming and terminate traction and dismantle the chamber.
As its is, there will be no scaring as fresh skin will quickly develop and heal to leave not even a hint of scarring. You should not pop the water blister but allow it to naturally break and dry up.
Keep in mind that you should take complete rest for at least a month as the new dermal layer will be vulnerable to blister again very easily in the same spot.
Take you time and learn from your experience to avoid the same again in the future.