No need to worry about work experience, it's not necessary. The course isn't about becoming a lawyer, it's about the Law.
Yes, it would be good to mention the residentials, especially what you got out of them - they are good evidence of 'super-curricular' activity.
If you reapply with A*AA your are statistically less likely to get in than someone applying in Year 13, who is statistically less likely to get in than someone applying with 2 or 3 A*s post-A level.