The Constitution is more of a compact than a contract, although it does share some characteristics with both. It's fundamentally a document outlining the structure and powers of government, created by and for the people, with the people ultimately retaining sovereignty. This contrasts with a contract, which typically involves specific, negotiated aagreements between parties.
The Constitution was not ratified bt the people, it was ratified by the states. The states agreed to the terms proposed in the Constitution, but less than one tenth of one persent of the 4 million people ever gave their consent.
Contracts require all of the parties to the contract to agree to the terms of the contract and all of the states gave their consent. while less than one tenth of 1% persent of the 4 million people living in the united States ever allowed to give their consent.