I'm scared to mail the nat cert...
I think I'll drive to DC and get the pp.
(is it only possible if you have emergency travel plans or can anyone do it?)
I think every new citizen goes through this. I also was scared to send away my certificate. I cringed when the postal clerk stapled it to my passport application. Fortunately, the clerk was considerate enough to put the staple through the white border, avoiding damage to the actual certificate part.
Since you must show proof of travel within 14 days (it can be an itinerary) and drive to D.C., I suggest biting the bullet and mailing your cert. Don't worry, you'll get it back.