ALTER USER [<username>] WITH LOGIN=[<username>]

Is the right approach.

Otherwise go to:

**Security > Logins > (your username) > Properties > User Mapping**

[![enter image description here][1]][1]

and remap that user to the database you want.

You can use the following query in the context of your database to check for orphans:

    select
        dp.name [user_name]
        ,dp.type_desc [user_type]
        ,isnull(sp.name,'Orhphaned!') [login_name]
        ,sp.type_desc [login_type]
    from   
        sys.database_principals dp
        left join sys.server_principals sp on (dp.sid = sp.sid)
    where
        dp.type in ('S','U','G')
        and dp.principal_id >4
    order by sp.name


  [1]: https://i.sstatic.net/WF8SU.png