I would think wondering how you will manage 26.2 is pretty much par for the course. When I did my first marathon last year I can recall wondering where the other miles would come from whenever I completed a long run... but they came. I reckon its all a building process and by the time of the marathon, with the miles in your legs and some freshness due to the tapering you will have the stamina to manage it. Trust your coach and the schedule, keep doing the miles and enjoy the challenge - it isn't supposed to be easy or everyone would be doing it
Nice to meet you too this morning Malcs... sorry I couldn't stick around after and have a coffee with you and your entourage. Sadly Xmas break finished at midday so I had to leave soon after the finish to get ready for work.