Ah.. toga parties. Been to quite a few, and hosted one. My advice, don't wear white. Since you're the hostess, stand out. Wear a red one, or blue or something. Wear something funny underneath.

Keep the booze flowing (assuming you're of age) and don't take it too seriously. There's going to be mishaps, people are going to break stuff, knock things over, fight, etc. and you just need to chill.

One thing I cannot stress enough, do not simply knot or tie your toga. PINS! LOTS OF PINS!