Congratulations! The money makes it an easy choice and you are to be commended for such an achievement,
Be aware that there are a lot of rich kids at Williams and that there have been reports out of Williams in recent years of students from ordinary financial backgrounds having trouble fitting in with their more affluent classmates - especially if they’re minorities. Coming in as a junior when the cliques are already formed won’t make it any easier, but if you know that going in, you can be prepared in advance.
Williams is a fantastic school with lots of opportunities to take advantage of. Best of luck!