Certainly looks like it has a week or so left. Candle the egg again in about 3 days, and show us some photos then. You’ll know it’s ready to be put into “lockdown” when the egg is almost entirely dark, the air cell dips up along the side, and you can see some shadowy and / or triangular-shaped movement (internal pip) inside the air cell.
Depending on what species of duck egg this is, you may not be able to keep the baby. Any wild, native species is illegal to hatch, keep, or tamper with, so you’d want to get them to a wildlife rehab right away.
If it’s a domestic or non-native duck, you could keep it, but you’d need to get them a ducky friend or two & do lots of research on how to care for them properly. Otherwise, I’d rehome the baby.