I think that the key is organization. Plan more than you will have time to cover, is there a way to involve your audience (game or questions), stack your samples etc. in the order you will use them, maybe make a list of what you will cover in time order (you could even put this on a dry erase board for all to see and then you would know how your aloted time is going). Try to talk slowly, it will probably be just the right speed.