With all due respect, your professor has let his own prejudice about Jesus influence his teaching, and you need to realize this. He wants to persuade you to believe (or disbelieve) just like he does, and has selected his material with this in mind.
What he told you isn't new; I encountered it myself when I was in college. The difference is that I had a brilliant professor who was also a devout believer, and he pointed out the error of equating Jesus with the mythological gods of the ancient pagan world. Your local Christian bookstore can suggest books to help you answer questions like this.
The key is this: Jesus Christ was a real, living person -- unlike the mythological gods. He lived in a real place; His actions were observed by real people; His life was carefully recorded by real historians. As one of them wrote, "We did not follow cleverly invented stories when we told you about the power and coming of our Lord Jesus Christ, but we were eyewitnesses of his majesty" (2 Peter 1:16).
Pray for those around you who don't know Christ, and ask God to help you be a bold but loving witness to them. Most of all, stay firm in your faith. Take time to pray and read your Bible every day, and ask God to help you find other believers on your campus to encourage and help you.