try putting the tacky tape on the bag first. place it one or two mm back from the edge. still use the painter's tape on the part, but the tape on the bag will cut down on the time the epoxy is 'out' before the bag is down. i have used both methods, the tape on the part and filling in folds and the tape on the bag. i did the first for about 20 years. after having used the second, i realize i wasted 20 years.