[Q] I entered the U.S. on visa waiver status, and my I-526 petition was approved shortly thereafter. Can I file I-485 now?
No, when you enter the U.S. on a visa waiver status -- the right conferred upon nationals of the Visa Waiver Program countries -- you cannot file I-485 even if you have I-526 approval. That's one of the benefits you are giving up when you enter the U.S. on "visa-waiver" status.
Except for limited circumstances where there are strong reasons why you and your family members cannot even come out to home countries even for 7 or 10 days or there are certain factors that may delay issuance of Immigrant Visas at the Embassies, we recommend consular processing over I-485.