I did the same. I created a group by mistake and there were very sensitive people in the group. Based on my experience below are the things you have to do.
Don't exit yourself from the group.
Change the group name (immediately) in case if the group name could offend some one. But do add in the description your message. Example "This group was added by mistake. Sorry. I am deleting you all from this group."
Then start deleting one by one from the group. Make sure you delete most sensitive people first (Because Whatsapp post a notification when you delete each member from the group. So if you delete the most sensitive people they will see only few notifications)
Once you delete every one, keep the group for couple of days in case if anyone contacts you. The reason being, I may be your contact but your name may not be in my contact list, In that case I just see one number added me to a group. In case if I need to contact you, you should be reachable and better by chat
In Case you exited from the group before doing the above steps: (You are going to have some hard time:concern:, still manageable) Follow the below:
Whatsapp will assign a new member (not sure what is their algorithm to choose the new group admin) of the group to be the admin of the group. Even if you have exited (but not deleted the group), you can see who is the new admin. If you have deleted the group by mistake then, call any one of the contact whom you know is there in the group and ask them to find the new admin of the group.
Call the new group admin and ask him to add you to the group and make you the admin. Some time Whatsapp may not allow to make an exited admin to be an admin again for sometime. In that case ask the new admin to add another number (Your brother, sister, wife or a friend who is near to you) to the group and make them the admin.
Then you access the group with your brother's account and delete every one separately. Finally when its you and your brother are the only ones in the group, you can definitely be admin and then ask your brother to exit the group.
You remain in the group for 2 days and delete the group.