High Speed Cruise Control - 115 mph

I was using cruise control successfully during my Nevada Open Road Challenge at 115 mph. I would cycle between 114 and 115. I had an iphone app that showed speed to .1 mph. I was nearing the southbound finish and decided to put the cruise control at 114 mph and just use the throttle to touch it a little without worrying about slowing down too much. I as about 180 msec behind. But when I got on the gas nothing changed. The high speed cruise control had full control of the throttle with no action by me. By the time I figured this out, I turned off the cruise control, floored it and picked up 60 msec going through the southbound finish at 117 mph.