This actually happens because the air gap between the raft and the print is too big, however, if you make it too small your raft will not come off. I recommend what most people say about a better build surface.
Personally, an 18$ glass build plate from amazon has worked wonders for me, better than any painters tape or buildtak.
I add a generous amount of hairspray and let it heat up to dry.
If you are interested, here is the link to the glass plate:
$16 unless I'm missing something