Hi, we have just installed a bathtub which will be used as a shower bath. after setting in the bath and adding the aquacheck plasterboard we have noticed the plasterboard is rubbing against the bath lip when we stand in the bath. we know the issues isnt coming from the mortar bed. we need some advice on how we can stop the plasterboard from rubbing against the bath lip? please note the bath and walls have been installed- next to do is add the tiles. thank you!