First of all, in Lite-C you have to define the type of each parameter, so it has to be
void on_level_event(var percent)
(It seems that the example in the manual doesn't write the "var" either. This seems to be an error at converting the code from Lite-C. Even if the compiler accepts your code without the "var" I do recommend not to ommit it.)

I guess you set on_level = on_level_event; right? on_level is only executed BEFORE the level is fully loaded, so the last value you get isn't 100, but rather 99.9 or something like that.
You have to define a function for on_level_load, which executes the code in your if (percent >= 100) block. Then it should work. And I also recommend to let that function execute on_level_event(100);