When I paint I use this tape, am I doing it wrong?

[your_slice_of_life86]

I paint with acrylics on canvas and I want to get a perfectly straight line. I'm painting a sort of jail house picture. I tried using scotch low tack artist tape and as soon as paint gets on the tape it curls up on the edges causing my edge to get RUINED. The painting is sitting over in the corner looking like major crap. Is there a better tape to use? Am I doing something wrong? Is masking tape safe to use? Will masking tape take off any paint that I've already put on?

 

[estonianmk]

i really don't know alot about tape but try this
use a different kind of poster board
use stronger tape ( not the kind that tears paper off easily.
try this also
tape a strip of paper down the paint over the paper
hope this helps!