What was your expected OG? I'll bet you just collected a sample (say, from the top-off water) that wasn't completely mixed with the extract. It's pretty hard to miss your gravity by much with extract.
Yea if you are doing an extract kit you pretty much can't miss the FG as it's all coming from the extract. Now U could add to much water at the end and dilute it but that's unlikely if you measure correctly.