If you've accidentally added a service more than once, you'll have to remove the duplicates. However, make sure not to remove the service you originally added, as you may have scheduled posts set to post to that service. Also, removing it may cause you to lose your reporting data.
The way to avoid this is to rename your services, and this will allow you to determine the which services you haven't scheduled posts for.
1. Go to Services - My Services, and find the services you'll rename.
2. Rename the duplicates by adding a number at the end (e.g Service, Service2, Service 3)
3. Once you have renamed them, go to your Scheduled posts, and check to see which service your posts are set to post to.
If you haven't scheduled any posts, you can check your Sent posts instead.
4. Once you have determined which service you'd like to keep, you can delete the duplicates, and rename the service you're going to keep, back to its original name.