You mentioned comments about the opening, but the fate of the game swung back and forth several times in the late endgame.
After White 235, you passed:
There are a few endgame moves left, so it's a bit early to pass, but most importantly, after you passed, white was able to kill the four stones in the lower left.
That capture cost you more than 8 points. Since the final score was White +7.5, losing those stones was a game-losing mistake. Let's take a minute to look at them.
Right now, white cannot cut:
But notice that black's capturing group on the outside only wins the capturing race by one liberty. That means if those black stones lose a liberty, this sequence doesn't work for us anymore (foreshadowing).
After you pass, white plays to cut, and you block like so:
After white connects with
, black has to connect with 
to prevent losing the large black group. So far your moves were forced. Then white plays this 
:It looks like this move is threatening to cut off your stones, so you responded with
at "a". Actually the cut doesn't work. Do you see why? Black does have problems though, since your left side has been cut in half. Those splitting white stones could be a real problem for you. Instead of at a, I think a move like b or c would look better, although I can't read out the whole thing.Now white plays 7. This is a scary play for black, because of that shortage of liberties earlier. Watch what happens now:
I'm not sure exactly the best way to prevent this, maybe a sequence like this:
If you're not careful white can still cause trouble here, but I think black should be able to kill the white stones, since both sides are independently alive. (Don't take my word for it!)
As it went in the game, you blocked on the other side with
, and white ends up capturing the four stones and also getting a ko to live, which luckily for you black was able to win.The pass, the unnessary block at
, and the wrong approach at means you had 3 chances to save those stones and win the game. As Bill says, endgame is about fighting strength.
M3. ( W has a weakness at J3. )
o2. ( Your M4 stone is light; if W wants it, let W take it;
M6 is a shared vital point.
- 
Terrible exchange for B. Problem in basic shapes.
, what's your plan if W cuts at E15 ?
, 
- 
W has the option to first atari P13 or o13 before connecting --
o14 atari.
R12. ( o14 atari still waiting. )
100 J7.
135.
should have been at Q10 to prevent 
. If Black has 2 corners and White has 2 corners, neither side is really falling behind. At this point strategic development is the most important thing, so no need to worry too much about local gains or losses unless their impact on said development is substantial. In the actual game White got to set up a base in what should have been Black's part of the board. Maybe White would have played at C10, after which Black would place H17 to disrupt White's moyo by afterwards jumping to either E17 or L17 and setting up base. My understanding of the opening is always changing, so consider this just one of several lines of play.
to 
gave White some outward influence, which was put to good use later on in the game. Playing 
at N5 would seem a better move as it avoids forcing White to fix up her weaknesses (something I saw a lot of in this game), while protecting the cut at N4. After this, play somewhere else such as H17, wherein Black can disrupt White's moyo by jumping to either E17 or L17 to set up a base. 
should be at E12, since the C12 stone is not worth saving at this point. 
is ill-timed since White is already strong in that part of the board. I would have played this at Q17 if I had to play there. The weakest White group on the board in in the bottom right quadrant and this group can be harassed to help Black gain territory. Why not play 
is a standard capping attack, the conditions are not so favourable. The way to handle such situations is to strengthen your position first. In other words, be patient.