At Move 51 you lost the game. When White was allowed to play at J2, forming a two eye structure in the bottom right hand corner, you had no chance of winning. White could have been undone at several points in the game, but you are still figuring when it is better to reinforce your shape for defense or to contest your opponents movement. The two biggest examples of this are:
Move 28: You played C2, but it wasn’t needed. You should have played B8, which would have killed his group. He would have been unable to turn that group into a two eyed structure.
Move 30: You played E2, but you should have played at D8, in order to prevent White from growing any further. Had you done this, even if White built his two eye structure in the bottom right, you would have won on points alone when the game concluded.
I wouldn’t pay too much attention to the AI at this point. Yes it is useful, but it is sort of like focusing on a GPS before you know how to drive. The GPS is always going to be helpful, but you don’t really need it. You cannot use it to it’s full potential until you first know how to navigate on a basic level.
Preventing your opponent from building two eye structures is crucial to victory. Especially on the 9x9, where games are fast and opportunities to grab territory is limited. I built this demo board a little while back. You might find it useful in helping you to recognize two eye structures on the 9x9 