#1. Practice out of air emergencies.
#2. I suck at physics, but the math is 120 +33/33 = 4.64 x .33 = 1.53, way too high a P-O2 for doing anything other than decompression at rest, in my opinion. You should have sat that dive out. It's important to be able to do the Dalton's diamond calculation on the fly if you're going to dive mixed gasses. For dives in that depth range, you need more gas than a single cylinder and 27 or 28% will be fine up to 130-140 with a max p-o2 of around 1.4. Destinations often get changed on dive boats and you're better off being prepared for a slightly deeper dive. If you take advanced nitrox/decompression procedures or the equivalant so you can decompress with o-2 and get out of the water in a reasonable time. Good luck!