What was wrong with my queen side castle here?

I'm a noob for starters and this was my second time playing the Sicilian intentionally. This is my one and only "good" game as black and I ain't going back. I'm in love and now want to learn.



10...O-O-O

Did I just castle too soon and maybe should have waited to see what side the opponent was looking to attack on? Computer says a4 push was a threat. My chess brain doesn't comprehend. I thought I was supporting my d5 pawn push.

In the Sicilian black usually castles to the king's side O-O, so as to push the pawns on the queen's side forward. c7 already is on c5, then b7-b5. After your 10...O-O-O white could prove your king is not safe there with 11 a4.
I disapprove of your 3...Bg4 and 5...Bxf3. You trade away your good bishop, bishop not on the colour of your pawns e7-d6-c5 for a mere knight.
Instead of 6...e6 I would have preferred 6...g6 intending 7...Bg7.
Your moves 8...Qb6 and 9...Ne5 were better 8...Be7 or 9...Be7 to prepare O-O. You should not bring your queen into play before your other pieces and you should not move a piece that already is into play a second time before your other pieces are into play.

Your king is too exposed on the queenside. a4 would have been a way for white to punish your mistake, because it forces you to create weaknesses in your king position.
I agree with @tpr that as a rule of thumb, you generally should not castle queenside as black in the Sicilian. (In fact, from personal experience, I have found that it is rarely a good idea to castle queenside as black at all.)
Bxf3 was also bad. Bishops are generally better than knights, and you should try to avoid taking pinned pieces, as you are trading an active for an inactive piece.
Bg4 wasn't very good in the first place either. Steinitz said you should usually develop knights before bishops and he is generally right. Nc6 does a better job of controlling the center.