It is impossible for you to fully rectify the harm that you have caused. Those who lost their lives due to the shots cannot be brought back to life; those who suffered serious harm will not be cured by your repentance; those who suffered economic devastation, estrangement from family, friends, and community might not recover what they lost.
However, it is still incumbent upon you to repent for your actions and rectify the damage to the best of your ability. Yehoshua bin Nun implored Achan to repent before his execution, even though he would still be put to death. Achan’s repentance brought honor to the Jewish people and salvaged his own soul in the next world. This is the same opportunity and responsibility that is before you.