I have a dark magic, and I’m not sure if the string is touching the sides of it while its on, and it might be shifting over to one side not sure if thats from bad throws for sleeps or what. Any help is appreciated
Work on your throw. 95% of the people that have that problem need to work on throwing straight. 
Yup, the throw will push it to the side.
However, once you get a yoyo with a flush response system (not an O-Ring, Starburst, or Duncan Friction Sticker, it won’t really matter.
And to finally answer your question, there is no way that I know of to put the string on centered. However, you can buy a KonKave or a Center-Trac Bearing and they will do that for you!
Its all about the throw, you could get a KK or a CT to center it for you, but it won’t improve your throw.
Fixed it for you.
I don’t recommend doing that. I personally despise KonKaves and Center Tracs. They’re tools that allow you to avoid a problem instead of fixing it. If you’re going to buy a nice, deluxe bearing, get a SPEED, SPEC, or 10 Ball.
If you want a centered string just keep working on your throw and you’ll be set.