I am by no means an expert or experienced so take this for what it's worth, but just sharing my experience to hopefully get you to a solution. I was having the same problem on my car doing a very similar patch with the exact same material. It was recommend to me to turn up the wire speed over the recommended level. I'm using an Eastwood Mig 135 so if the recommended wire speed was 3, I turned it up to 3.5. That seemed to solve my burn through issue and I was able to go back and weld up the pin holes very nicely. I can share some pictures later if you would like.