Some OSs protect/reserve certain Ctrl+Key combos, so your system might revert Ctrl+Q to Quit after changes. Try something else like Shift+Q and see what happens...
Alternatively, if you haven't installed SketchUp properly SketchUp might not be able to remember user's changes to shortcuts in their preferences file.
This will be obvious if changing a shortcut to something potentially innocuous isn't remembered across sessions.
To fix a faulty installation is simple.
Exit SketchUp and find its Installer exe file, usually in your Downloads folder.
Select its icon and right-click > context-menu > Run as administrator
When the dialog opens it should offer a 'Repair' option.
Choose 'Repair' and let it run,
this will fix the permissions of various files and folders,
so that your normal user-accounts changes to things like Shortcuts are remembered between sessions.
Choosing to 'Run' the installer's exe file, or double-clicking it is not the same as 'Run as administrator', even if your user has some admin-powers.
There's no need to Uninstall and Reinstall to fix things.
The Repair will not affect any customized changes or extension installations etc...