A screen shot is your best option. With a decent resolution monitor it should be more than good enough for anything that is then viewed on another screen whether in photo or video format.
Cropping to the round corners will be no problem with a vaguely decent image editor (no cost options included)
Just had a skim read through this and it covers most of my normal steps.
If you are hoping to print, that is a different matter entirely. You want to max out any settings you possibly can and then hope for the best frankly.
Depending on how much resolution you need, and how much time you want to give it, it is worth working out whether your phone might give you a better resolution image.
The 3rd option, which requires getting a little clicky with settings, might give you enough to head towards print quality. Also worth considering what file type you are creating the screenshot as, where you have a choice!
Frankly, once you work out these options, they will probably provide you with a better mock-up, with more flexibility than you would get from Glide producing something.