how do I stop safari from automatically zooming in by itself

Doug, just asking this --Are you using a Magic Mouse? And is it possible that you are absent-mindedly tapping on it while you're waiting for pages to load? Or while you're thinking?

If it's not a Magic Mouse issue, from your Safari menu bar click Safari > Preferences then select the Extensions tab.

If you have any installed, turn that OFF, quit then relaunch Safari to test.

And check settings in System Preferences > Accessibility > Zoom

Yahoo!

That's exactly what happened to me.

So glad you're all sorted now.

😉