You may have your page zoomed with a feature built into Chrome -- zooming out and in is done by holding down the CTRL key and pressing the ' - ' or ' + ' key. If that hasn't solved your issue, you may have certain accessibility features turned on. If you head over to the bottom right corner, click on where it shows the time and battery. A new box will show up with a few different options; choose the accessibility settings option. There will be a magnify setting, along with a half magnify setting that are likely checked. Uncheck those features, and the magnified screen should return to normal.