how can I prevent printing an incomplete fillable pdf in adobe acrobat?

Short answer: You can't.

Longer answer: You can't, but what you can do is force a warning message to appear on the printed page, and/or to force all the fields in the file to be empty when it is printed. To do that you would need to use a script, like this (paid-for) one I've created that sets it all up for you: https://www.try67.com/tool/acrobat-validate-required-fields-before-printing-or-saving

Not possible.

You need to ask program questions in the forum for the program you are using
To ask in the forum for your program please start at https://community.adobe.com/
Moving from Using the Community (which is about the forums) to the correct forum