A CNAME already exists with that host. (Code: 81054)

I want to add a subdomain in blogger but why when I want to add a blog subdomain and point to the blogger ip always like this, is it my fault? help A CNAME already exists with that host. (Code: 81054)

The message is pretty self-explanatory. As evident from your screenshot there already is a “blog” record and, it being a CNAME, you cant add another such record.

In your particular case, that one CNAME should be enough.