Is it permissible for me to benefit from the money remaining from the car accident compensation, after repairing the car at a cost less than the compensation amount?

If the value of repairs and damages is estimated by experts or the competent authority, then it is permissible to take the full amount. Any surplus remaining after the repair is rightfully yours, because what matters is the judgment of experts and specialists. Compensation includes damages and the depreciation in the car's value after the accident.