I have only built on one Forecast blank(7'9" 3wt), it's a very nice casting rod, and I have only heard positive reviews of their blanks.
Is it possible that you received a mislabeled blank, and it's really a 6 wt? You can run a Common Cents test on the finished rod to determine the line weight. You can find the information over on rodbuilding.org, top left link will take you to the CCS database where you can purchase a copy of all the articles explaining the system and how to run the test (very simple) for $4.00. Before I junked the rod, I'd test it. After all, you have invested some money and a lot of time in the build.