installing 36x36 pan into 37x36 framed opening. 36 from entrance to back wall. 37 from side to side leaving 1/2 inch gap on each side. it seems that the existing dry wall above the shower side walls will not match up if pan is centered in opening. or do I push pan into corner and leave a 1 inch gap on one side wall and deal with that. ANY help would be great. First time for shower install and any info would be appreciated. thank you.