The OEM gasket has nothing to do with 6 holes unless your engine came that way from the factory. Seadoo makes 0.3mm to 0.8mm gaskets and which one you need is determined by the clearance between the piston dome and cylinder head known as the "squish" clearance. To do it correctly you need to measure this clearance then choose the correct thickness gasket to get you within the spec clearance.
The aftermarket gasket companies only supply one or two thicknesses to save them money from making and stocking multiple thicknesses. You can probably get by with a 0.5-0.6mm gasket but this is not always the case.
To little squish clearance and you will melt down the piston from detonation and too much clearance an your engine will be a dog.
It is not like a Yamaha where there is only one gasket and it the same from any supplier.