I had the same problem with my sniper plate on an AP kit.
I used the pot of boiling water trick. Took it off the boil, dropped the sniper plate in for a few minutes. Turned on the cold water tap, took the plate out held it wider apart and straight under the running water. Did a test fit and repeated the exercise.
It worked a treat as the plate was now wider and gave a closer and more even fit to the shin. When it came time to glueing it to the shin, I still needed to use a heat gun to get the ridges either side to line up a bit better and give me a slightly flatter surface to glue to. I used Zappa Gap to glue it, one side at a time.
I did use zip kicker on the last side once I was sure it was as well aligned as it was going to be.
Hope this helps, and good luck.
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