Sorry to sound harsh mate but you were going to a part of a recruitment process for a job that you really want & you ran out of petrol & gas?
Not very good PPPPPP is it? (Prior Preparation Prevents Piss Poor Performance)
And you also signalled your volunteer work takes a higher priority than a potential paid one!
Most employers would have not given you a second glance (unless of course you have certain skills that others don't & even then not for a lower level position, think specialised middle or senior management).
At least next year you get another chance, so good luck & make sure the car is full
As I said it sounds harsh, but when you are starting at the bottom, they can afford to be choosy
cheers