FULL backup takes care only about data pages from data files.

It does not touch TRN log file at all.

You need to release some sppace in log file by doing BACKUP LOG, and only then you'll be able to shrink it.

But it's not that simple.

You can only shrink TRN file if latest LSN entries (Virtual Log Files) are "inactive" (check Status returned by DBCC LOGINFO, "0" is iactive, "2" is active).

1st BACKUP log will inactivate all the VLF's up to the latest one(s) whcih are in use by the current transactions.

You need to wait until SQL Server "loops over" and starts recording new transactions from the beginning of the LOG file. You will see Status=2 appear for the VLF's at the beginning of the TRN file.

Then you can run BACKUP LOG again, and if the VLF's at the end (check againg with DBCC LOGINFO) have become inactive then you can shrink the file.