Welcome to the forum
If you have Nero installed, you should be able to finalise your disc. If not, ImgBurn (free download) will do it for you:
With the disc in your PC drive, open up ImgBurn, and I believe the option is in Tools --> Drive --> Close.
I don't have ImgBurn on this PC, so I'm just going from memory - if I've left anything out, hopefully someone will explain further.