No, if you're only getting one login, you're not running it as SA. You need the rights to read the logins from the source server and the rights to create logins on the destination side. Make sure you have SA rights. DBO is NOT sufficient.
I always review the output of sp_helprevlogin because it DOES list ALL logins, including already built-in logins such as SA. I like to comment out the ones I don't need so I don't get the spurious errors.
Once you run sp_helprevlogin, you shouldn't need to do anything else. Your user databases and their sysusers tables all work off SID. the nice thing about sp_helprevlogin is it reproduced the IDs exactly, including the SID & password, so all the user access should automagically reappear. It's a really cool tool.
Speaking of spurious errors, make sure you examine the output carefully. Some logins will invariably fail. The most likely cause is the SID is already taken, or the login name already exists, but with the wrong ID. You'll need to manually fix them, most likely by dropping the user login and maybe from each database and then recreating it manually. You can use the sp_helprevlogin code as a template to recreate the adjusted user ID. So, for example, you can recreate it with the same password.
One last caveat: sp_helprevlogin does not handle roles. So if you are moving DBA logins with SA rights, they will appear on the destination with no SA rights. You'll need to manually add that in yourself. You can massage sp_helprevlogin to handle roles, if you wish (I need to do that one day!)