Judging by how hard you left off the gas/nitrous, or hit the brakes (only 4 mph gain in the last 1/8th mile?), I'd say you were probably on a low-mid 14-second run if you'd have stayed in it. Your 60-ft time isn't all that spectacular, though.
I gain 20mph in the last 1/8th mile usually. You need to make a full, complete run. That's the only way you'll ever find out.
I hate sandbagging, too. It can work the other way, though, and you'll still lose. I got 2nd place at an import event this summer by launching, spinning, and thinking I was behind because of the spinning I did on the line.
Soooo....what do I do? I stay in it -HARD- to play catch-up, which I think I need. I ended up breaking out. So did the other guy. If I'd have just let off anywhere on the track (or before the lights, as I didn't catch the other guy), I'd have won the event.
Such is bracket racing...