https://www.verywellmind.com/imposter-syndrome-and-social-anxiety-disorder-4156469
I wouldn't take too much stock in what your friend is telling you. You've earned your place at your school, you've done the work and you've earned your grades through your own hard work and diligence. You're not expected to know every little thing right at the get go. You've said it yourself, you're still technically in the middle of your first semester. Don't beat yourself up over the things you don't know because in time you'll learn it anyways. It's normal to learn that you don't know anything at all as you expand your knowledge set.