It's totally up to you, but I really don't understand the need to be prepared ahead of time. Prepared how? Clothes and decor? Those are really the only gender-specific things, and it's pretty easy to get clothes after the fact (you'll probably get lots of clothes as presents, and besides, gender neutral things exist for a reason!), and nursery decor can wait since the baby won't be in his own room at first. Unless you're super DIY and know you won't have the energy to decorate later, I suppose.
But if you really want to prep ahead of time and also would like to please your DH and yourself if you want to stay surprised, there are tons of really adorable gender-neutral themes for nurseries out there. And then you won't have to deal with worrying that the u/s was wrong! (Yes I know the chance is small, but I'm the type to worry about that stuff no matter how small the chance.) PLUS then you get to re-use the nursery for any future baby.