Good luck Kenny. You sound talented, mature, and determined, which is a great combination.
As for your question, top 100 or 200 U18 quality in America will certainly get you a tennis scholarship. However, the caliber of tennis program could be quite different depending on how high up you are (which determines facilities, coaching, fan base, internal and external competition, etc). A top 20 player will be playing at one of the elite programs, while a player ranked #200 might be playing for a tiny division 3 school.
http://www.tennisrecruiting.net/ can you give an excellent barometer of where you stand if you are familiar with any of the other players that are listed on an annual basis.
Also, do bear in mind that you are competing not only against the US, but the rest of the world as well in trying to get a scholarship into the better programs. Some programs don't even have a single American in their top six, and some tend to recruit primarily from certain countries (i.e. a French head coach and assistant picking the cream of the crop in France, etc.). Keep working hard and good luck!