The powerful Public Accounts Committee said costs could still spiral as industry has no incentive to keep them down. The project remains "high risk" with unresolved technical problems creating the potential for "uncontrolled growth" in the final bill, it warns.
In 2010 Chancellor George Osborne accused Labour ministers of mismanaging the contract as it would have cost more to scrap the boats than to build them.
But the MPs' report warned that three years on, the Tory-LibDem Coalition Government "has not yet completed crucial negotiations with industry over the carriers". It added: "The current carriers' contract is not fit for purpose as it fails to provide industry with any real incentive to control costs."
Labour's shadow armed forces minister Kevan Jones said: "Ministers have failed to learn lessons from repeated criticisms of their carrier debacle. Government plans for the carrier programme remain unreformed and the country will not be confident that costs will be kept under control."
The report said basic mistakes were made in the original decision, including the omission of inflation and VAT.
MPs also raised concerns early warning radar system that protects the carriers will be delayed by two years, limiting where one of the ships can travel.
Margaret Hodge, who chairs the PAC, said: "The committee is still not convinced the MoD has this programme under control. It remains subject to huge technical and commercial risks, with the potential for further uncontrolled growth in costs.
"To avoid making the same mistakes again, the MoD needs to start planning now for the next Strategic Defence Review in 2015, including making sure this time it has the right information on which to base decisions."
The SNP's Westminster leader and defence spokesman Angus Robertson said the report was "yet more evidence" Westminster makes the "wrong defence decisions".
Defence Secretary Philip Hammond insisted the "not fit for purpose" criticism was levelled at Labour. He said: "We are negotiating with industry to seek to secure proper alignment."