Bring salty snacks and water and you should do *fine.* It's 46 miles, not 406. The other thing I'd suggest is that you ***relax*** -- if you're worried and stressed about not going fast enough... that will affect your body position and your blood chemistry (like looking down when you're climbing a mountain) and deplete your performance. Relax and decide that you'll either go fast enough, or you won't, but you'll do your best to look like you know what you're doing... and you'll find yourself going faster than if you're looking at the speedometer and worrying.