It's possible you have zoom enabled and are inadvertently using a gesture to toggle it on
check your settings, go to settings > general > accessibility. Is zoom on? If you're not visually impaired, you'll most likely want to turn it off
If it was on, it's possible you were toggling the feature by double-tapping with three fingers on your screen at any point. When zoom is activated, the gestures of the phone change, even for normal navigation. You have to use 3 fingers to move around the screen when zoom is on.