All you need to do is go into your map,
and put the mouse on the ground where you want to spawn in the map, and in the box on the bottom of the screen, it shows some coordinates.
Write them down. If they have a huge decimal, you don't have to write anything down after the .
Now go to the first tab in mapmaker if you aren't already there.
Check the "Has Portal" box, and type in the coordinates that you wrote down.
Save and your portal will be in Cape once you log in, and it will take you to whichever coordinates you wrote down.