uhuuu !! congrats !!
You are brave !! I´ve been scuba diving for about 4 years now, and always run away from the cold water, there is this place in Brazil, called Arraial do Cabo, considered the second best place to scuba dive in the country, after Fernando de Noronha, but the water is a bit cold by brazilian standards, so in one of my dives over there the water hit 10 degrees celcius (about 50F), and I ended it up staying 3 meters above the pack, where it was warmer (60F) ...
Ohhh, I can´t wait to scuba dive again this holiday ... I´m going to Brazil, and will hopefully find the time to do it... maybe we can trade our impressions afterwards !
Have tons of fun in Mexico !!!