heres a couple pictures of my turbo i have on the car now

its a t04e a/r 50 compressor housing with a 50 trim wheel with a stage 3 turbine wheel machined in the ct26 exhaust side

im not using the ct26 actuator but another rather a just slightly bigger actuator off of a volvo t3 turbo which has the adjustable rod. i have the wastegate set up on the turbo to open up at around 14psi. which i did test it with the air hose comming from a air compressor set at 14psi and the wastegate was opening fine(this beening check when the turbo was mounted on the manifold and the downpipe wasnt on. but im getting over boost im creeping past 17 even up to 20 psi sometimes and i will hit fuel cut i do have the hks fcd. but sometimes it cuts at 18psi and sometimes it cuts at 20 psi. is the boost supposed to creep like that i just changed all the vac lines on the car and there is no leak. i dont think exhaust on the car can make the psi creep that much i have a ko 2.5 dp and a ko 3inch dual muffler exhaust.
current mods on car is - apexi power intake, berk tech I/C, KO 2.5 DP, 3" KO exhaust with the 7" mufflers, HKS SSQV, NKG Copper plugs
1.do you think this turbo can run 20 psi?
2.Why im a getting so much boost creep?
3. should i just weld the wastegate port on the turbine side and externally gate it with a tial 38mm welded onto the stock manifold?