scouting would've been a good idea. That way, you see what your opponent is up to and you can adjust yourself appropiately. As zerg, I would send a suicide overlord scout periodically to do this. Other than that, you're good. It was your opponent that didn't start gathering until much later in the game and thus he was behind. Building more than pylons when he could built a gateway. Ohh well. Overall, it was your opponent who did really bad. Try not to spend so much on mutli-tech(that is stick with one type of tech unit until later in the game) especially gas heavy hydras *and* mutas. That's the primary fault of zerg. Muta/lings is a good start.