This mod is no longer required as the devs have implemented the possibility to warp to suns into the game.
This mod was for game version alpha 9.4, which was many years ago.
You haven't done anything wrong, this mod is just retired but I kept it listed for posterity.

It may still be possibly to convert a planet into a sun star, though. Not sure it is necessary, but it is possible. The major issue is you couldn't land on the planet that was converted to be a sun star. It was mainly intended to serve as a sun replica so you could warp to a "sun".

I cant load the mod cause I cant click on start. What have I done wrong?

I think it is pretty awesome that the devs have created warp-to suns in Alpha 12 and the new nebula system is awesome! It's all coming together nicely and I like to think this little mod started it all. Gas planets are cool, too. Maybe one day they'll create new structure types that can be built in gaseous orbits, like gas harvesters(helium/etc).

Note: After some more testing (after some sleep!) I don't think that it is actually possible to warp from one sector to the sun sector, even with my modifications. I think there may be some hard coded limitation in the game blocking warping to this sector. I've tried all I can to get it to be able to "lock target" to warp in a CV but about the only thing you can do is teleport there as admin or perhaps use the playfield with a teleport from another playfield (which would be acceptable). If you have a different experience or know of the fix, please contact me! Thank you.
Perhaps one day we will be able to warp to the sun just like we do in Eve Online! Meanwhile, enjoy what we can.