bend over backward

bend over backward or lean over backward  {v. phr.},  {informal}

To try so hard to avoid a mistake that you make the opposite mistake instead; do the opposite of something that you know you should not do; do too much to avoid doing the wrong thing; also, make a great effort; try very hard.

Instead of punishing the boys for breaking a new rule, the principal bent over backward to explain why the rule was important.

Mary was afraid the girls at her new school would be stuck up, but they leaned over backward to make her feel at home.

Compare: GO OUT OF ONE'S WAY.