It's pretty tiny in the grand scheme of things. Wikipedia says it's 30ft long, 14ft wide and 9 ft tall (https://en.wikipedia.org/wiki/Boeing_X-37#Specifications_(X-...). The space shuttle was 122ft long, so around 4x the size. When you don't need to put space station modules inside the payload bay, or humans in the cockpit, you can make it pretty small and hard to find against the vastness of space