This is entirely my responsibility.

Meaning

Taking complete ownership of the mistake.

Examples

• John: 'This is entirely my responsibility, Alice. I should have been more attentive.'<br>
• Alice: 'Okay, John. Let's figure out how to correct it.'
• John: 'Thank you for taking responsibility, Alice.'
• Alice: 'This is entirely my responsibility, John. I apologize for the error.'<br>