Thank you all for your replies.
To be honest, in my letter with the mistake, I attached an html file regarding my TOEFL score. The professor asked me if I could provide her with my iBT scores in order for her to act for the prompt review of my application (I need as soon as possible a review because the demand of the Greek State Scholarships Foundation).
My iBT TOEFL total score is not very high, is 68/120. With this score and the mistake, I am starting to worry seriously for my impression (and for my admission).
Postscript:
Is a TOEFL iBT total score of 68/120 good enough?