IPS panels

Hi

I am.wondering if anyone has any experience with IPS. So the problem i am facing is, we received IPS panels for toilets but the cutout for the flush pipe was small. Req. Size was 28mm, cut out is 26mm. We are using victory flush valves and it comes with whole assembly including a piston so I don't think we can reduce the size of the valve. Is there any way we can increase the cut out size for the IPS instead?

Thanks in advance.