If you hate cold water then get a wetsuit, 70 is cold to swim in for any length of time and will drain your energy if your not used to it. My suggestion is to get a wetsuit and get out there at least a few times before your race. Practice running in and diving in such a manner you don't lose your goggles. Run in till you can't lift you legs over the water then dive, if your hands still touch the bottom, the "porpoise". Simply stand up and dive in again(head tucked between your biceps, hands together forming a point) and glide through the water till you stop, stand up repeat till you can swim without hitting the sand with your hands. Practice siting as well, every 10 strokes or so, give an extra kicking effort(so your lower half does not sink), then pick your head up briefly and try to focus on a land mark or buoy and maintain course that way. When you exit, don't try to run through the water till you can lift your legs over the top, generally, swim till you start hitting the sand with your hands. Good luck!

-Anthony