Is saying the pledge of allegiance in the U.S. at school to the flag idol worship?

No, it's not idol worship, but just like his religious allegiance, so too a Jew's national allegiance is really towards the nation and State of Israel, and you should always keep that in mind. In general the welfare of Israel and that of America are almost always intertwined and overlap, but should the US government change directions, as it sometimes may seem recently, it's important to keep your Jewish nationalism as your real top and eternal priority and allegiance. Jews have only been in America for several generations, and we know that all exiles out of the Land of Israel have been temporary, and that our real, eternal & unconditional homeland is the Land and State of Israel.