No, it would be ridiculous if Lexus voided the car's warranty for going a certain speed. However, if you redline the engine (make the RPM go above the redline on the tach dial), that could void the warranty. These newfangled cars have onboard computers that log things like max RPM, and if something happens to the car's engine and he takes it to the shop, they might plug it in and read that the RPM went over the redline and tell him it's out of warranty - and you're in big trouble if that happens.
However, I trust you didn't redline it. Right? If not then you're probably okay. Just be more careful next time! What if a cop pulls you over for going double the speed limit in your dad's new car? That's game over right there.
If you're really freakin out about it, you can always call a Lexus dealership and ask their mechanic over the phone. That would be anonymous of course, and you could just ask him flat out and he would be able to tell you for sure.
Good luck kiddo, you and I are cut from the same die.