Better to just use the unc path.
But if you insist on using mapped drive, then you have to map it for the SQL Server service account.
You see the mapped drive because it's mapped for you, but that doesn't map it for any other login -- in this case the service account.
As for xp_cmdshell
EXEC sp_configure 'show advanced options', 1;
EXEC sp_configure 'xp_cmdshell', 1;
GO but it is better to leave it disabled unless you absolutely need it. Know that it ALWAYS runs in the context of the service account, not the user account that executes it.