Okay, here’s the problem with being a dilettante. I seem to have screwed things up. 
I had the laptop in what I thought was a reasonably secure state using a Local Group Policy as described in the OP to limit what an ordinary user could do (along with some additional steps recommended by others here). But then I realized that I needed to make some changes while in logged in as that user.
Not being familiar with how Local Group Policy settings work, I thought and hoped I could have more than one set of policies and toggle between them. So under the Administrator account I created another Local Group Policy for standard users that undid all the restrictions of the first policy.
When I clicked on that, sure enough, everything was back to normal as regular user. 
But unfortunately, when I clicked on the original Local Group Policy, nothing changed back. None of the restrictions I had set up were in place anymore. 
I tried deleting the second policy, but the first one still doesn’t work.
Is there anyone here who is familiar with how Local Group Policies work who can tell me
- what I did,
- how to fix it, and
- how to achieve what I was trying to do, namely switch between a regular user having normal full access, and having the restrictions I originally set up.
Thanks.