SQL Server log file is too big
The log file won't get smaller when doing transaction log backups, but it will clear up space internally.

The only way to make the physical file smaller is to shrink it and expand it to a suiting size again. I'm guessing you also have some VLF issues with that size too.

Edit: You should do regular backups to keep the log from expanding again.

You could run something like this to check how much of the log file is in use:

SELECT
   name
   ,type
   ,size/128 AS [size_mb]
   ,FILEPROPERTY(name, 'SpaceUsed') / 128  AS [size_used_mb]
FROM sys.database_files