How many maps have you made before? If you haven't made many, I suggest starting small.
what is the scroll height and width?
SCALE: for really large maps, like the one I have that is 5000x5000, try 8000 to 12000 and save often, load up the map until the distances are manageable/playable to your liking. Mine is set to 10000 for that massive 5000x5000 map, but something else might work for yours.
Remember, you can create massive maps like that, but remember it'll be a whore on your CPU to play it if it's heavily populated by npc's, pirates, etc...