Hey Mel,
Don't worry - you will have a FANTASTIC time. I do know what you mean though about having organised it - you will feel responsible if little things aren't quite right. Well, you should not feel like this (though I understand why you do

)
What I always try and remember is that sometimes things don't go to plan but that's not necessarily a bad thing - sometimes you just have to call a time out

and go with the flow.
Example. I was in Epcot with my DH and 2 DD's on a VERY hot August day two years ago. Both my girls were very tired and grumpy and behaving less than perfectly. Obviously, what I wanted to say was "you ungrateful children, don't you know that mummy and daddy have brought you thousands of miles to have a magical time in WDW? Start acting like you are enjoying it!" (actually it is possible that I did say this or something along these lines

) But instead we rented a stroller, popped them in it and decide to wander around WS. Now, I was very put out about this as it was NOT on the plan and would mean we would not have time to do Test Track, Ellen's Energy Adventure etc etc at all that holiday. But clearly the girls were no longer having fun on my plan and I have to say the next 4 hours wandering round WS were possibly the highlight of my trip. Although we hadn't wanted to "waste" time like this. LOL, how wrong was I?!!
Sorry, this very rambling tale is meant to say - don't beat yourself up if things don't go to plan. Sometimes it's for the best!! Little things will go wrong but it isn't your fault!
Whatever happens, you will all have the time of your lives. Relax (make time LOL) and enjoy!!
Best wishes,
Karen