How to accurately bolt post anchors to existing concrete pad

[pepsp]

I'm upgrading an existing pergola and adding a deck at the back of our house. I'm having trouble getting the diagonal locations of the post stirrup holes right compared to the locations in the pryda stirrup base so I can bolt it down. You can see from the image below the hole is not quite centred compared to the base of the stirrup.

Any tips on how to do this correctly? And how to fix the one I've messed up?

[pepsp]

Just wanted to share a photo of the finished product. It was another low level deck project...

 before

 

 after

Thanks @MitchellMc for your timely advice!

[Jason]

The deck looks brilliant @pepsp. Great result! Thanks so much for coming back and sharing a photo of the finished project. I'm sure it will inspire other Workshop members. 

Jason