My shift key toggles running instead of hold to run, how to fix it

You can navigate the constellations with the keyboard using the WASD keys, which may be easier than trying to use the mouse , which have a tendency to click on the wrong star.

If you have problem reaching a star, you should try approaching it from another direction, like going from the side, or even another constellation.

This has always caused me problems before I figured out the controls - you have to hold Shift while jumping for the Prince to grab onto ledges. When he grabs on, you just have to pull yourself up by pressing Up.

Also as noted, since there is no room for a run up, you have to carefully get to the edge and then jump from the spot.

EDIT: To clarify - walk slowly to the edge, stop, and simply jump, without any running. During the jump (while you're flying) hold shift and you will grab the ledge.