Thanks for your replies, the wedding is tomorrow, I cannot refuse at this stage
I like to think I have good composition skills, I have my nikon d3200 which I will take as my second body with a 35mm slapped on.
I usually take all my photos without flash, how essential is flash?
With respect, if you are choosing to do something you have never done before, - a job where there will be no margin for error whatsoever, and little forgiveness for mistakes as it is an important day in someone's life, as everyone else has already pointed out - why on earth are you using a camera you are not comfortable with?
It seems to me that you are setting yourself as many hurdles and obstacles as possible; you don't do stills photography, you are not familiar with flash, you are photographing one of the most important days of someone'e life and you haven't a clue how to go about it, and you are choosing to further handicap yourself by bringing along a camera with which you are not familiar.
Worst of all, you have crossed the boundary between friendship and commercial transactions. This is not win-win, i.e. 'easy money' because it is a friend who might be less demanding. If anything, this could be the opposite.
Now that it is a business arrangement, it will be judged as such, and your standards will have to be even better - that means delivering photographic standards as good as the pros, but informed - and lit by - by your personal friendship with the person getting married.
At the very least, bring along someone else who knows what they are doing as a reliable back up. And use your own camera; this is not the time for experimentation. If you are not familiar enough - and you won't be - with a strange and unfamiliar camera to photograph swiftly, surely and flawlessly tomorrow you run the risk of - frankly - making an absolute mess of things. You don't want to be the topic of conversation in twenty years time when an embarrassed ex-friend shrugs through her wedding album with apologetic but annoyed words along the lines of: 'Oh, we made a total mess of that; we got in a friend of mine who knew a bit about photography but it turned out to be a disaster.'
Re flash, what other sources of lighting will you have? Will you be visiting any of the venues in advance to check out angles, sources of light, ambience? If not, why not?