Inclined platform concave and alters roll

The putting surface is good and the roll is pretty quick. However, the inclined platform is concave, causing all putts to veer towards the center. This means missed to the outside bend right into the cup (at least for the regulation sized cup) and putts on the inner edge of cup veer to the right and miss. Not sure how to correct this, looked underneath but not clear hoe to prop up the middle to make it a level junction on the platform. Everything else is good, ball return is nice, but with the curve it is hard to tell if you hit the ball straight, which is kinda the point.

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