This is imposter syndrome and literally everyone at every level experienced it at one point or another.
First, it is very bad (I might say, the baddest) to approach science as a competitive endeavor. Science ought to be collaborative, especially in the same group. If the professor is critiquing you it’s because he wants you to do better. If you are having personal issues and can’t handle the pressure then maybe this isn’t the right job or the right time for you. That being said, just try to relax and know that the bar for you is not really that high but clearing it requires you to make a genuine effort. Learn from the people that are better than you in the group.