Next time run
make all-depends-list before you start building the port.
If you don't like what you see on the list don't go any further.
This and other gems can be found in
/usr/ports/Mk/bsd.port.mk. Not friendly reading though.
You're mildly screwed in terms of cleaning up the mess.
You really have two options that I can think of:
Option 1 - Run the command above, figure out what you don't need, and uninstall it.
This is probably the least painful option.
Option 2 - run
pkg_info -aR and look for packages with no dependencies.
Determine which ones you don't need and uninstall them.
(This is a good housekeeping practice every year or so IMHO, but it's annoying.)
In terms of cleaning up the build detritus a simple
make clean in the offending port's directory should trigger cleaning of the dependencies. You can also do a
make clean in
/usr/ports, but it's probably faster to blow the tree away and re-extract it with
portsnap if you want to go that route...
As another (dirtier) option that's very specific to this situation: If you know you haven't installed any other ports since the "mistake" and the last time you installed ports was a while ago you can use the create dates of the directories in
/var/db/pkg - Simply remove the packages whose db entries were created around the time of the aborted install.
As with the other options above you'll still need to look at the packages you're removing in order to make sure you don't blow away anything important, but this should be a substantially shorter list than the other two options if it works for your situation.