I'm not sure waht you're masking, but here are a couple things for future reference.
Cut the tape is very small strips for the edges. It will hold complex shapes much better that way.
Aim the paint flow (assuyming rattle can or airbrush) away from the taped edge so the pressure from the compressed air will not push the apint under the mask as much.
If using a rattle can, hold it farther away than usual, dissipating some of the air pressure and pushing less paint directly against the edge of the mask.