Creating a new variable that is an average of two out of three measurements

At least with your sample data the result is numeric (double), not logical, so to help you with this you would have to provide a minimal REPRoducible EXample (reprex). A reprex makes it much easier for others to understand your issue and figure out how to help.

If you've never heard of a reprex before, you might want to start by reading this FAQ: