Nerves, oh nerves

I've been training for an endurance duathlon and am really frazzled at the moment. It's on Saturday. Can I do this? I have no idea. My stomach has cramped every time I've done a longer brick workout when I try to switch shoes. I've having nightmares about getting flats or going over on the bike. I'm worried I won't be able to run. I think it's just in my nature to worry. Man, it's something hard to get over. I'm sure once I'm out there I'll be fine. I'm riding the bike one final time today. It was raining this morning so I've postponed the ride until it clears up a bit.