So a bit of advice. There's an old adage, "When in doubt, lead it out."
It's actually a great piece of advice IF it's executed properly. Too many racers, especially non-sprinters, take that to mean, "Sit on the front for the finale, and wind up the sprint from 500-1000m out because I'm not super explosive." Which is pretty much a recipe for finishing 20th. As a pure sprinter, I'm just delighted when a non-sprinter decides to take it up early.
So what does it really mean for the non-sprinter? It means engaging the sprint from about 250-300m, maybe 3-5 seconds before "REAL" sprinters really want to go. If you're going from 250m, you'd do it from 3rd or 4th position. If you're trapped further back, you have to go earlier, but you really have nothing to lose. Leading it out from 250 from the FRONT pretty much never works for non-sprinter-- it's too easy for everyone to react and see the early sprint. The only riders who can legitimately lead it out from the front early and gradually, (often called a razor) are powerful sprinters with a decent amount of range. However, if you go from 250-300 from good position, you'll most likely get a good placing, maybe a podium, and perhaps even (rarely) the top step-- despite being a "slowtwitch" rider.