How to calibrate Garmin Vector 2 power meter pedals with a Wahoo Elemnt computer?
It seems others were having this same issue and it turned out to be the torque not being set to specs (Garmin recommends a torque of 25 to 30 lbf-ft (34 to 40 N-m). 

In my case, I had skipped a step in the Wahoo calibration. Here's the fix:

1.) turn your pedals 1 rotation so that the pedal pods blink 5 times in a row (this means garmin is ready to be calibrated).
2.) Turn on your Wahoo Elemnt by pressing and holding the power button. Once on, press (but don't hold) the power button to get the to the GPS/Sensors screen. Select your sensor and in the bottom left corner you should see CALIB. Press that and it will complete the process. 

I just got back from a 3mi test ride and my watts went from 257w to 118w (which is much more accurate!).

Hope this helps!