Move confused me. Even if O11 doesn't look urgent to you, why did N15 seem like the biggest move on the board to you at the time?

- Marty Lund

... which I had misread...

I hope that clears your confusion about my choice.

Yes, that does clarify your choice. Thanks.

Seriously though, have you realized that is probably the losing move? The thinking behind it turned out to be wrong: both tactically and strategically (in that the top is not the key to the game). Black was strong at the top and therefore could absorb whatever White might do there with little real effect. Meanwhile Black had many weak points in the center, which White used to devastate Black's position. Issues of strength and weakness are normally much more important than territory in the middle game.

I understand what you mean but I'm not sure what to do with the strength in the center.

11 is a mistake. It worked out okay in game, but it shouldn't have. Having gotten this far you need to play K17.

Here's the thing:
1. If you want more claim on the top (which is what you say when you play O16), you need to finish it off with a move at K17 or thereabouts. If you don't play here, and white approaches your corner, you pretty much have to respond for very few points, and white can lightly jump back and claim most of the top. That is, you're leaving a sente play for white. One that's big enough that white could probably take it immediately (if you don't respond, white can scoop out your base, and now you have a weak group on the run).
2. If you want sente to approach one of white's 3-4 stones, play O16 at O17 (3rd line). That gives you stability and you can take sente. Alternatively, you can just ignore white's approach to your 4-4 and approach one of his 3-4 stones.
3. You shouldn't reasonably expect to get sente out of approaching the bottom left corner. Generally speaking, the approach-er to a corner loses sente. The fact that you did get sente feels like white made a mistake.