What to do when a home improvement costs way more than the original estimate? I had a bathroom built in my basement?

It's about 7 feet by 8 feet. Porcelain tiles everywhere. There is also some new electrical wiring in the basement. Early on in the project we got an estimate for $12,800. I realized the tile installer was pretty expensive so we got a much cheaper one to do the work. Bathroom is complete and looks great but I the bill shot up to $17,000. The main reason is that the general contractor took a lot more hours (he's a carpenter) to get his work done. I'm being charged for those extra hours he didn't anticipate. I think this is wrong. What are my rights as a homeowner in this situation. Also my mortgage is paid off if that makes any difference. And how do I fight a lien against my property if it comes down to that?

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