First, get a console in your qube via Qube Manager and run lspci -nnk to ensure that the driver have installed successfully and is being used.
In general, with fedora you need to either:
- delete X config entirely if you want qubes gui integration for CUDA or maybe Optimus Prime
(see this guide) - create an entirely new one if you want to have a complete desktop
(see this guide and this message in particular)
You can also check my guide on deploying qubes for CUDA loads using salt.