Good opening, but bad follow-up (12k)

Hi! I played this game:

I think I had a good opening. However, I failed to use it to my advantage and I’m quite lost as where I went wrong.

Can someone help me with obvious mistakes?

Thank you

I’m just a little more strong than you, about 8/9 kyu.

I tryed help with some variations and concepts, but my moves can be wrong for more experient players.
I hope that it help you.