Ways to combat boost creep Options

[6G94celica]

Ok so before my car died my boost gauge at the most i ever noticed read about .9 bars. calculated thats about 13 psi. i bought an upgraded ct26 with a larger compressor wheel from brashboy on ebay. im not sure what the wastegate is set at but this seems really high. i dont want to wreck anything internal and only want to run about 8 or 9 psi. also i have a custom 3 inch exhaust that i personally built with a high flow xlerator muffler with a single 3" inlet and dual 3" outlets. i know im running some major boost creep and am wondering how best to stop that and add some backpreassure to the turbo to slow freewheel.