My baby measured about 15 ounces at 19 weeks, 4 days. They told me that's still within range. She's just a big baby. Both my husband and I were big babies. When they estimate weight, that's all it is, an estimate. Babies are born different sizes.
Your due date is probably off, my son was measuring big my whole pregnancy and technically came a month early but he was full term. I'm pregnant again with my daughter and she's measuring big too.