How screwed over am I from going to a competitive high school

You are definitely not ‘screwed’. My son’s prep school had over 50% of the class accepted at Michigan - and not everyone applied - some with GPA’s well below Michigan’s 25th percentile! It is all about the high school. Michigan State accepted nearly 100% of applicants and turned around admissions decisions in ten days under a special program for his high school. Colleges definitely favor certain high schools.