No, your house was not a US Obligation. An example of a US Obligation would be savings bonds. The US borrows the money and is obligated to repay it.

The U.S. did not borrow money for you house.You must pay the tax.

I filed my taxes with the state of Maryland and there is a error. I deducted the capital gains from my income and I was not to do that. How do I correct the filing?

Since you already filed your return, you need to amend it to make the correction.

Here's how you amend your state return:

1. Sign in to your account.
2. Scroll down to Your tax return & documents , select 2019 and then Amend (change) return. 
3. Select Amend using TurboTax Online.
4. Select the reason you’re amending and continue.
5. Answer the questions about your federal return, even if they don't apply. You'll eventually get to the screen Let's get started on your state taxes.
6. Keep going and we'll present you with the option to amend. In some states, this appears right at the beginning; in others, it appears towards the end of the state interview.
7. When finished, we'll provide printing and filing instructions for the amendment. Your state may take several months to process it.

Amended return can't be e-file, you need to print it and mail it in.