Here is one line that works for White: 21.g14 22.i19 23.g18 24.f18 25.h20 26.h17 27.k19 28.j20 29.j19
I tried a few moves for Black, don't see an answer. Tell me what you think.
21.g14 22.i19 23.g18 24.f20 25.j21

There are some pretty complicated lines starting with |21.g14 22.g21 but it's definitely tighter. And I don't like Black's chances trying to beat White in the top left, especially with how much you outplayed me in the top right.

Twixtbot says if |21.g14 22.i19 then 23.g19 24.g20 25.e18 and then Twixtbot pretty much gives up on that corner; apparently White has won it. If |21.g14 22.g21 then 23.i20 and again, White has it.

In fact, if we back Twixtbot up to |21.g14, it gives up on that corner immediately. And if we back it up to |20.g16, Twixtbot comes up with 21.g14 as its best move.

The game is far from over at that point, though. Here is a long continuation from Twixtbot:

|21.g14 22.h10 23.f10 24.g8 25.e8 26.f4 27.m13 28.f14 29.r15 30.s18 31.e13 32.i19 33.e18 34.k13 35.g7 36.h5 37.i6 38.j6 39.k7 40.l5 41.l11 42.s4 43.t6 44.u3 45.q5 46.p3 47.n4 48.m4 49.p2 50.o5 51.r3 52.r8 53.t10 54.e17 55.g19 56.g18 57.k19

(White wins, but I don't trust lines that long)

All of this points to the fact that G14 is the move I missed. May not have been a slam dunk, but it is what I should have played. Thanks all for the input!