My school would never predict anyone an A* at A level unless you got over 90% in as...even then I had to ask (nicely) for an A* prediction in a subject I got 100% in!
I don't think it should be 3A*s, (I actually don't agree with the whole predicted grades things), since people always getting predicted A*s, simply because they got an A, undervalues those that have shown the potential to get it at A2. I'm not questioning your intelligence by any means (those are great as!) I'm just pointing out that the A* grade is actually a lot more rare than many would make you believe. I wouldn't worry too much about it anyway! The predicted grades you've got are still brilliant and put you in great stead of being a competitive candidate for top universities!