My zoom features is zooming in way too much - Lr

I normally can click on a photo and get it to zoom in for more detialed eidting. Howeve,r for some reason, when I do it today it zoom in way too much, to the poiint where the picure is pixelated and unreadable. I don't recall hitting any buttons or settings, but I must have done something to cause this. How do I undo it?

Thanks.