Here are 4 different ways to align your map on Roll20. When hovering over your page, click the Gear icon for the Page Settings dialog.
Click the “Page Toolbar” (it looks like a page icon in the upper right of the main area). Click the “Upload” button in your library to import the image.
Hidden Rolls - have the player make blind rolls, and only the GM see the result. Roll20 Tips and Tricks (Innovative Solutions to Common Problems) (Forum) contains a large amount of tricks and examples of clever uses for macros etc. Photo-based, nearly-tileable hex textures for Roll20, mapmaking. Hex World: Realistic Hex Textures for Maps. I think it typically defaults it to a tiny 2x3. Then drag-n-drop the uploaded map onto the map layer in Roll20. Switch to the map layer (I sometimes forget this, whoops!). Create a new page along top at roughly about the ratio of the image.
Nature Pixels a top-down pixel art asset pack that can help u build your game world the way u want! Gowl. Nature Pixels | Top-down pixel art asset pack$3.40-66%. The maps cover a wide range of sci-fi settings, from ship rooms, station corridors, barren moons, alien jungles, ice planets, desert planets and even the depths of space among others. This bundle contains an array of 37 sci-fi themed mats to keep your crew rolling through any unexpected encounters.