I followed the guide on here and smoothed my bumpers out using the expaning polyfiller and u pol on top method as in the DIY guide thing is it's started rising before ive even put on the primer and basecoat

so i've dug it all out now i was just wondering what i could do, i really want smooth bumpers, If i take it to a bodyshop rougly how much would it cost? also are there any other good methods that works, any ideas anyone?
Many thanks
Anis