How to secure yellow tongue floating floor to concrete slab?

Hi,
I have started to lay the new flooring in our new house and the southern rooms have gone well.

I firstly removed the skirtings; rolled out builders plastic as a moisture barrier, then layed 19mm thick yellow tongue boards ,gluing the joints together; on top of which I have secrete nailed 18mm pre-finished maple boards.

However, when I initially placed out the yellow tongue in the rooms with northern / western glass doors (ie not properly fitted, but just dropped on the floor as a temporary measure to reduce the concrete dust), the heat has caused them to slightly warp. Thankfully, the damaged boards have not actually been fitted yet, but I'm now concerned that this will happen again, even under the protection of the maple flooring.

I guess that I could mechanically secure the yellow tongue, but drilling through the builders plastic would compromise the effectiveness of the damp protection and would also increase costs and time. I would also have to find a fixing that could be countersunk into the board.

I can't glue the boards to the concrete if I wish to use the builders plastic in between.

Any thoughts on what I should do, or if you think that the yellow tongue will remain suitably stable once covered over?

Cheers, Paul