Alternately, I've found you get a lot more freedom of Panning around the page if you make the Roll20 Page much larger than your intended Map, and put your Map somewhere in the middle of the Page. Create margins for yourself, giving a lot more flexibility in scrolling any direction. In your situation I would like to recommend trying this method. Example screenshot of this, 25x25 map area inside a 220x180 page at 30% zoom, giving you lots of extra margins so that nothing is appearing to stretch or float, and you won't even see the grey-hatch background unless you scroll far to either side. In this technique you set your own background color in the Page Settings.