I tried making a colonial administration in Senegal, but it immediately became independent, hwat's up with that?

That's strange that this is happening to you; that issue should be resolved in the current version. By any chance, are you using an earlier version of the game? because this mod only works with version 1.8. Or maybe you're using a mod that doesn't have the subject type 'Colony' or 'Chartered Company'?, it could also happen that you're using an older version of this mod. In that case, I recommend unsubscribing and subscribing again.

I was playing on 1.7.7 Maybe it'll work on the latest version. I'll have to try it.