Unfortunately, law schools offer "accidental" scholarships. It happens.
The problem with your case is that you didn't really rely on the scholarship offer. You made up your mind about going there before you got the scholarship award and the scholarship award didn't significantly change your position. (If the award was unexpected, you should've checked with the law school immediately.) Yes, you turned down other schools but you'd already turned the other schools down anyway.
If you'd actually made your decision based on that award, you'd have a stronger case. (Although I'm pretty sure that even then law schools reserve the right to withdraw scholarships and even offers of admission.)