Are you nuts? Someone just handed you $200,000 to go to college! This frees up resources for your parents so they can pay for your sibling’s school. Usually, two kids going to private school doesn’t end well for the parents. If they’re already paying for your sister, then nothing is different. You have a guaranteed scholarship in writing, and those are numbers you can depend on.
A NPC is not reliable. It’s just a ball park estimate that can change from year to year. When actual financial aid numbers come in, it’s very common to be short-changed.