Hello,
Can you go into a bit more detail what you are trying to do? If you are setting this up through a script, I would suggesting using the metadata to grab the anchor IP.
You can grab it with
curl http://169.254.169.254/metadata/v1/interfaces/public/0/anchor_ipv4/address
and it will return the anchor IP for the droplet. This would allow you to set this directly as opposed to setting a range that can vary based on region and other unpredictable factors.
If this doesn't work, please go into a bit more information on what exactly you are trying to do and perhaps a more specific solution can be offered.
Edited for errors.