They won't try to charge you when you check in. However, anytime between now and check in, you may very well be moved to E- seats by a computer sweep if you haven't paid for them and aren't entitled to them for free. If I were you, I'd check your itinerary fairly frequently, so in case you are moved, you can at least change to more desireable E- seats (if you don't want to pay for E+) before they all go, too.