Patio sub base screw up

I'm building a 4x4m patio for the back garden, so the load will be light, no vehicules or anything like that. Some of it's going on top of old concrete, some of it I've dug away the top soil and intend to put a sub-base down. The intention is 100mm of sub base (or the pre-existing conrecte) then 40-50mm of mortar, then 22mm stone slabs.

Here's where I might have screwed up - due to a bit of a misunderstanding on my part I've had delivered 3 big bags of 20mm ballast delivered (along with 2 bags of sand for making the mortar). I know that Type1 would be a better sub base, but can I make do with the ballast? I'm not sure that I can return it.

Thanks in advanced!

 

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