I tried a few more times today. There was a lot spaced out gusts so the kite would go up quickly for about a minute then fall slowly. It flew decently high though, it just needed a more constant wind.
The conditions where not optimal but I tried to fly the kite with a 50 g load. Just to see if it would take off. Even with the strongest gusts I didn't worked. I guess it would have been too easy with such a simple kite, so now I have to find a better kite design. I don't know much about kites so if you have some suggestions feel free to comment.