They needed a lot more than that. They needed healthy people in general to sign up, and many either already had coverage, or didn't want it. That, or were too lazy to try to get it.
From the beginning, it was said that ACA would pay for itself. That of course was bullshit, but the administration knew that with the taxpayer funded coverage of losses for the insurers who went into the program, it would have a few years to start working. They didn't like to talk about this part, but nobody was in the dark. The losses were not however getting better, and therefore, the Republicans I believe passed a rule that stated that taxpayer funded coverage would be not be allowed, calling it (rightfully) crony capitalism. ACA was supposed to take profits from successful exchanges and use them to pay off the losses from the failed ones. There were not enough successful exchanges to make this work.
The plan was fucked from the beginning. Had the bailouts been allowed to continue, personally, I don't think the ship would have been righted. But there is disagreement about that. There wasn't much evidence that the situation was improving. United recently pulled out, and there isn't much to make me think that there will be an improvement in the near future.
If the government was in better fiscal health, much like say, Massachussetts was with RomneyCare, they could have absorbed the losses better and might have been willing to stick out.
I don't have a better solution, though. Single payer is the only thing I can think of, but with our government's track record, I can't help but think they would massively fuck it up.