It is not just how much you weigh that makes you still look pregnant. It's also how much extra skin is on your abdomen and it takes longer than 3 weeks for that to shrink. You've gained very little weight actually. I think the placenta alone weighs around 12-15 lbs. You can wear spandex panties or a girdle so that you look more trim.
Do not restrict your eating now. The weight you gain during the last month is all baby weight. You want your baby to be a healthy weight.
One of the mothers of multiple baby births looked good on their TV program but she was still wearing a firm girdle years after their birth. She finally had a tummy tuck to get rid of the extra skin. With a singleton your body will absorb the extra tissue but it takes time. A firm foundation with as little weight as you've gained should take care of the extra.
I've had several abdominal surgeries and it took 2-3 months for my abdomen to flatten out again. Surgery causes bloating. Organs have been moved around and they take time to settle back into place.
A more realistic approach than losing weight is to go shopping and buy a flattering dress; something A-line without a waist; something that fits at 3 weeks post birth. Wearing a dress with a flattering cut takes lbs. off of our appearance.
Then for pictures stand sidewise at an angle. Not completely sidewise. Also, if you take the baby holding the baby will block the view of your middle and remind viewers that you did just have a baby.
Take Shane's message to heart. Your figure isn't important. I know we want to look our best. You will look your best post pregnancy. Those who love you will be so excited about the baby and seeing you they won't notice your tummy. And you can camouflage it somewhat for pictures bt wearing a good fitting and flattering dress, standing slightly sidewise and placing yourself slightly behind someone else..