What do I do if there is an error in a figure in my not-yet-defended thesis? I submitted my thesis some days ago and I am currently preparing for viva. I have found an error in a figure which is a summary of four other figures. In fact, by means of Excel I did calculations and made a mistake regarding some numbers. I have prepared a new file with  corrections but I confess that I am scared. 
Anyone has experienced such a situation or may give any tip about what to do.

Thank you very much indeed
Speak to your mentor. However, I see no reason to panic or to be scared, if the mistake doesn't influence some fundamental contribution of the thesis. I've found numerous cases where mistakes in the thesis were found years after the defense, even with considerable impact (one extreme case de facto made ~60% of the thesis obsolete aka wrong).

If the thesis is completely printed/prepared/submitted, I guess that the mentor won't insist on repeating the process.

Again, this is not a great issue, if the error is not of fundamental nature (e.g you base your thesis that the actual value of pi is 4, but somehow you miraculously discover now that you were of by 0.8584).