Go here and register:
https://does.pflbas.dc.gov/vosnet/default.aspx
They will contact your employer to confirm salary, and they will tell your employer what they paid your (so your employer can make you whole).
Note: you will likely need different forms for DCPFL than the ones your doctor filled out for your STD at your employer.
Also, your employer was supposed to give you this information (if they are DC-based). Whether you choose to report that or not is up to you.