Calf cramp & century ride on Sunday

Dooh! I was screwing around on a "social" paced ride last night and ended up giving myself a cramp in my left calf. Was on a downhill and decided to see how fast I could go. Dropped into my largest gear and started hammering away. Towards the bottom of the rather long (but shallow) downhill I got a nasty cramp high in the left calf. I had to nurse that leg through the remainder of the ride or it would cramp back up (luckily only had 4 more miles or so). Today, it is sore. I cut my planned run from one hour to only 30 minutes and did some calf stretching and light calf raises to hopefully work it out. i have a 101 miles ride Sunday and am worried that this thing may cause some problems, specially later in the ride (i.e. miles 80+) when things tend to go to he77 anyway. What should I be doing to nurse this thing back to health. I'm unsure if ice or heat is right here? Planning on continuing some stretching and massage as best I can tolerate it (I really hate leg massages, freaks me out for some reason). Thanks for any input & advice!