Please make sure you are adding the correct record as changes of CNAME record might need at least 4 hours of propagaion period.
You could like to add record as below where will point docs.domain.com as CNAME to ghs.google.com.
docs IN CNAME ghs.google.com.
1. Log into HELM Control Panel.
2. Seek for your domain.
3. Select on DNS Zone Editor.
4. Select "Add New" for new creation or click on the old record that need to change for modification.
5. Please use the format as below.
Record Type: CNAME (Name Alias Record)
Record Name: docs
Record Data: ghs.google.com.
Record References: 0 * MX records only
IMPORTANT: Record Data of ghs.google.com. end with a dot(.)
6. Click on Add/Save.