You can not 'retract' a statement once it has been made. All you can do is to make a second statement saying why the first one is wrong.
A common mistake we hear it all the time, and it is on TV programs, but the truth is once made the statement remains as evidence, and can be used in court. You need to make a second statement saying why the original one was wrong with all the details about being under morphine, being pressurized to make a statement and not remembering what you said.
Get a solicitor or independent person to witness the second statement .