IIRC, it starts counting lines from the start of the batch that created that proc. That means either the start of the script, or else the last “GO” statement before the create/alter proc statement.
An easier way to see that is to pull the actual text that SQL Server used when creating the object. Switch your output to text mode (CTRL-T with the default key mappings) and run
sp_helptext proc_name
Copy paste the results into a script window to get syntax highlighting etc, and use the goto line function (CTRL-G I think) to go to the error line reported.