offer a 0.1-0.9 point split
Unexpectedly you matched up against a Grandmaster, your first move?

your first move should be..., resign. :)
seriously though, you're going to lose. so why not learn something from it?
picking up a gm in a game is absolute gold.
as chexpert said, take him off the main lines early so you're not playing parrot lines. (unless you know the theory, how does that assist you?)
just play your best based on sound opening principles. try and analyse every move in as much depth as you can. start by looking at his move and asking yourself, "why did he play that?"
in fact as a rule, never concentrate on your own plan. look at what your opponent is doing first, then look at your own plan. (it's a good habit to get into. too many times i've got caught in the beauty of my own ideas only to get caught out by the beauty in others.)
then watch him slowly dismantle you. analyse the result in detail and ask yourself "how did he tear me apart? what mistakes did i make?"
i suspect the game will end swiftly. but watching him work will be poetry in motion.
at the end of the game. why not ask him for feedback? don't understand why he play a particular set of moves? ask.
you might be surprised, he may just answer you. what do you have to lose in asking? and his feedback may be priceless.
see this as the great opportunity that it is. :)
I'd blindfold myself. Just hate to see myself get slaughtered that badly. :-)