Advice on scope mount setup for RPR w/ Vortex viper PST FFP

So I took my RPR 6.5 creedmoor (w/ vortex viper pst 4-16x50 ffp) out for the first time today to zero at 100meters. I zero'd well with hornady 140gr factory loads. However when I went to set the zero stop i noticed I had to use basically all the shims to stop the windage at zero. Also the index line for zero reference lines were on like 3 instead of 0. I was reading that this might be related to scope mounting and not having any cant with like a 20moa rail. I currently have vortex precision machine rings on the rifle, however I have an american defense manufacturing quick release mount with 20moa cant in my parts bin. Would this be worth swaping to the 20moa qd mount/would it rectify the zeroing issue with the shims and reference lines? Would the ADM mount be solid and secure enough for a precision rifle setup?

It should be secure enough for your precision gun.
As to-“rectifying the zeroing issue”, I’d assume you just need to try it and see.

Those vortex precision rings are some of the best out there. Call vortex. Their CS will help you out.

I'm certain they will give you additional shims. Two things, have only had to use half of the shims on various rifles with or without angled bases and you will find they will compress until they are seated. Meaning that if you are counting on having x amount of elevation under "0" you will need to add shim(s) after you run it down to the "stop" a few times. More than likely you won't be able to have an exact amount anyhow. The shims are ok and the PST II system is marginally better. Nothing beats the NightForce Zerostop in my opinion.