Dear candidate, yes you can undo your mistake. NTA will intimate all students about the image discrepancy which must be corrected by students. Any modifications or corrections to the photograph/signature can be done using the login facility given by NTA or even with the correction window from January 15 to 31, 2020. You can follow the given below steps to correct your mistake -

• Click on the 'NEET candidate login' link provided here
• Enter the NEET application number and password
• The option to upload the photograph/signature will be displayed on the screen.
• Upload the correct images as per the given specifications.
• Verify once before submitting it.
• After submission, an OTP number will be sent to the registered email ID and mobile number of the candidates
• After the given OTP number is entered, the NEET correction slip will be displayed on the screen.

All the best

Hope this helps