You are asking us to diagnose your taste buds online!
Green = Hay / Straw
Sour = lemon / unripe green apple
Underdone = Woody / Cardboard
Bitter = aspro / grapefruit
Burnt = Chargrill / Ash
Attach a picture of the roast, it will help CSrs give you some clues.
If I had a guess I would say that what you thought was 2nd crack might have been late 1st crack.* 12 minutes in a popper seems pretty long but it is cool outside so that would add time to the roast.
Best bet in a popper is to sacrifice a roast, take it way too far, black and oily... then you will know what too far is and can back off a little.* Its pretty common to roast too light when you start .
PS: C1 and C2 is hard to read for other newbies, please use the extra key strokes for 1st and 2nd.*
Less TLAs = easier to read. ;)