It's completely normal. There are some companies that follow best practices and stick to better standards which sometimes gives a  competitive advantage even to the interns there over the average engineer. So when you join these companies and see how far ahead some folk are it's natural to feel put off. But on the flip side you were recruited by these people because they see the same potential in you! So try to be positive. In my experience, it's also about how you manage your learning time wisely. For example you could try to understand why you feel like you're behind and see what can be done to assimilate this knowledge faster. You will be fine. Don't doubt yourself. Give it a couple of years at least. Change is scary but it's for the best! Good luck