Hair simply changes as we grow up and unfortunately you can't do much to stop it - nature always has its way lol.
My hair is the perfect example of this:
SUPER curly when I was a toddler (and I mean I had ringlets with 70% shrinkage), then when I was eight to eleven it was wavy and BOOM when I turned twelve it went back to rocking ringlets. I started straightening my hair / doing chemical treatments then and now at 22 I'm finally embracing my curls. Thankfully my hair has stayed curly, so I'm hoping it won't go changing again.
Also, that's not to mention the way my hair changed COLOUR. I had dark brown hair when I was a toddler, then it went to a dirty blonde colour and then seriously bright ginger and now it's a really deep, dark brown again lol. (Seriously, it's ridiculous haha. No hair dye needed for me!).
Point being hair as a life of its own. Saying that though, lots of people say their hair gets a lot curlier when following the CG method, so maybe with a good routine your curls could be here to stay?
I'd say not to worry and just embrace what you've got for now