Hi Sophia
Nicely done! You've progressed really well since I last saw/heard anything from you, which is probably down to me not being on the forum much, rather than you not posting.
I don't know what's in the sheet music as I don't own it, but you're right to start adding in your own variations and improvisations. As I've probably said before, if you work through all the books in the series, and at the end of it you still can't play a 12 bar blues without having some music in front of you; you've really missed the point. Or the books aren't doing their job.
That said we all have different talents and levels of natural ability, and when it comes to playing the blues it just may not suit some people.
Cheers