ive played slap bass for 27 years and i can tell you i've had my fare share of blisters and bleeding fingers. My advise to you is to burst it by sticking a needle all the way through so there are 2 holes to dispell the liquid and dip your fingers in either witch hazel or surgical spirits once a day untill you build up your callous' which takes time. Another suggestion is to use surgical paper tape if you feel your fingers are about to blister.
good luck!