Flyscreen frame mounting problem

I bought a fly screen kit and have built the frame and splined the fly screen. It came with an offset button. The problem is my flyscreen mounts from the outside and theres no place to put it. My original fly screen came with spring pins. The new flyscreen doesnt have holes for spring pins.

Is there an easy way to securely mount the flyscreen frame? Just to reiterate it mounts from the outside so it would fall outwards if knocked loose, not inwards.