The trick is not what you say, it's how you say it. Say your short prepared bit, and then just tack on the end - 'Ladies and genglemen, please raise your glasses and drink a toast to --- and ---, The Bride and Groom' and lift your glass and drink, then sit down and breathe a sigh of relief! Before all that, have a few practice goes at it. Keep your head up, breathe deeply, make eye contact with a few people in the room, look at the B and G as you name them. Speak slowly, and clearly, and raise your voice without shouting, so the whole room can hear you. Keep it as brief as possible, and smile! You'll be fine. God luck.