I decided to make a review as a bit of an experiment and practice for myself, even though I'm a few stones weaker than you (~8-10k depending on the day). Therefore, take everything I say with a grain of salt if you see a problem with it.
I saw three potential problems with the game.
1. Opening Theory -
In general, Corners > Approaches/Enclosures > Side Extensions > Invasions / other middle game stuff.
At move 14, you ignore this order and invade directly.
Without established bases on other parts of the board that would come from a normal opening, your invasion group had no support. Therefore, it had no friends to run to, and black could chase it into the center to strengthen his stones and profit.
2. Prioritizing Territory over Weak Groups
In particular, moves 28, 42, and 44 stuck out to me as wasted opportunities to save your weak center group. While all might be fine in normal circumstances, it's bad timing when you have an extremely weak group on the board. ( The bottom was big, but reducible and smaller than a dead group...)
Even if you thought your center group could survive a fight if necessary, these moves allowed black to keep attacking it severely - making huge profit on the top and bottom center.
I can't help you much with specifics (since I'm terrible at it...), but I can tell that you could improve your fighting significantly if you improved your understanding of shape.
Dwyrin's videos are great for this - especially his "Back to the Basics" series (designed for SDKs mainly) if you haven't seen them
Hope some of this is helpful! Feel free to let me know if you see any problems with any of the things here or in my review (you are stronger than me after all...)