hmm k, do not panic:)
you always have this option and your db is not huge, i'm sure all is salvageable.
check it out:
http://www.phpbb.com/community/docs/INS ... pdate_full
4.i. Full package
The full package is normally meant for new installations only, but if you want to replace all source files this package comes in handy.
First you should make a copy of your existing config.php file, keep it in a safe place! Next delete all the existing phpBB3 files, you may want to leave your files/ and images/ directory in place. You can leave alternative styles in-place too. With this complete you can upload the new phpBB3 files (see New installation for details if necessary). Once complete copy back your saved config.php, replacing the new one. Another method is to just replace the existing files with the files from the full package - though make sure you do not overwrite your config.php file.
You should now run install/database_update.php which, depending on your previous version, will make a number of database changes. You may receive FAILURES during this procedure, they should not be a cause for concern unless you see an actual ERROR, in which case the script will stop (in this case you should seek help via our forums or bug tracker).
Once the install/database_update.php has completed you may proceed to the Administration Control Panel and check remove the install directory as advised.
4.ii. Changed files only
This package is meant for those wanting to only replace changed files from a previous version to the latest version. This package normally contains the changed files from up to five previous versions.
This package contains a number of archives, each contains the files changed from a given release to the latest version. You should select the appropriate archive for your current version, e.g. if you currently have 3.0.6 you should select the phpBB-3.0.6_to_3.0.7-PL1.zip/tar.gz file.
The directory structure has been preserved enabling you (if you wish) to simply upload the contents of the archive to the appropriate location on your server, i.e. simply overwrite the existing files with the new versions. Do not forget that if you have installed any MODs these files will overwrite the originals possibly destroying them in the process. You will need to re-add MODs to any affected file before uploading.
As for the other update procedures you should run install/database_update.php after you have finished updating the files. This will update your database schema and increment the version number.