When you want to say sorry in Chinese, you use the phrase '对不起'. It is pronounced as duì bú qǐ .
对 (duì), fourth tone, can also mean right or correct
不 (bú), second tone, meaning no, or not
起 (qǐ), third tone, is a verb, meaning get up.

If you want to express that you are really really sorry, you can add '真的(zhēn de)' in front of '对不起(duì bú qǐ )' .
真的(zhēn de) means really

真的对不起 (zhēn de duì bú qǐ) means really sorry.