Do you have 4" pipe to connect it to? According to their website (which is hard to navigate for specs) these push in flanges only fit this size pipe. probably to prevent undersizing the drain line. When I have installed piping for future use in concrete floors, I always used rubber or styrofaom around it. This allowed a good seal, no chance of the concrete breaking the pipe and also room to remove some of it to install the flange.

 

Im pretty sure its 3" pipe but yes it has a styrofoam cap around it to protect it when poured.

I thought I saw a slip on flange that was for 3" pipe on their website somewhere. I jsut though that would be easier than trying to glue something else on, just slip it in screw it down and go.

 

Oatey makes a floor flange that will slip into and tighten up inside a 3 inch toilet drain pipe, and from my experience tightening their standard "Twist & Set" floor flanges into 4" PVC pipe, it's super secure and I'd trust it in my own building.

http://www.oatey.com/Plumber/Shared/ProductGroupDetail/363/Twist-N-Set%c2%ae+Cast+Iron+Replacement+Closet+Flange.html

Note that the Twist-N-Set PVC floor flanges come to fit both 3" and 4" ID pipe.