When you sell real estate the capital gain is calculated as your proceeds from the sale, less the basis, plus improvements, and less any commissions and closing costs. The tax at the federal level is currently 15%, and your state will have a tax due as well. If you do not pay the tax when due, and you properly filed the return, the taxing authorities will begin collection procedures which could include levies upon any assets you may have. You should consult with a tax professional if you cannot pay the tax and discuss the options available.
Any individual seeking legal advice for their own situation should retain their own legal counsel as this response provides information that is general in nature and not specific to any person's unique situation. Circular 230 Disclaimer - Advice given in this response cannot be used to eliminate penalties with the IRS or any other governmental agency.
Your capital gain would be the sale price (600K) less your basis in the property (565K). You would only owe tax on 35K (assuming the above figures).
THESE COMMENTS ARE NOT LEGAL ADVICE. They are provided for informational purposes only. Actual legal advice can only be provided after consultation by an attorney licensed in your jurisdiction. Answering this question does not create an attorney-client relationship or otherwise require further consultation.