Uneasy feeling during the first day of school

As what had mentioned, this was the first day of my last semester. I entered 2 classes but they ended up with 2 different outcomes.
The first one was pretty fun. I met back my previous lecturer and I was pretty excited to get to learn new stuff from him again. Besides, I have enough confident to approach a high distinction for this subject......if possible, but I will try my best and I wont let him down.
The second class was a total opposite from the first class. Her introduction of the subject was considered O.K. to me. In fact, this subject is more to analyzing numbers and making decisions. I'm sure I can cope with that. Later on, she mentioned about accounting and the four big companies. Being as one of the future accountants, I hardly know any one of the big four approaches while she had also mentioned that those who are interested in accounting SHOULD know this. At the very moment, I was wondering, am I suitable or well-prepared enough to hold on my current ambition to be a professional accountant and own a accountant firm in future? In the past, the answer was very obvious and it was a big, proud YES. But now, I really dont know.
I admit that I'm that kind of person who easily being influenced by other people's words. Its just sometimes I cant think and my mind will be blank.
I need opinions from others. I hope I could find some answers regarding to this.
Somehow, I think I should change my mindset. Be more open-minded to other people's words to avoid hard feelings in myself. Sometimes, I just cant do that, especially talking about my future.
I really afraid I had chosen the wrong future. No doubt that I have lost some of my confidence in me. What am I going to do?! Stick to me current dream or choose another path?
I really hope he was here with me......I just need someone to stay beside me now......