Online exams and in text citation, will i fail?

I had an online exam recently, and we were asked to provide in text citations but not reference list. Due to pressure of giving the exam and writing my final dissertation thesis, I accidentally wrote the wrong author’s name but the right year for one of the citations. I mixed up the name with an article for my thesis, it was a case of slip of mind. I have mentioned the right author and year in the previous para. I noticed the mistake only after submitting the paper and it is a 100% weightage exam. I’m afraid I will be failed for this. Will i be failed or will they deduct mark for poor citation? Should i write to my professor about the mix up?