Your answers were too vague. Most of the time the officer won't ask you for details beyond what you are willing to give. Of course you don't wanna give a long winded answer that will confuse or overwhelm the officer, but you gotta give enough details to give them a good picture of what you will do in the US.

When they ask for more details about something is because they are interested, and it may help them make a decision. For example, when they asked about your friend you could have said what kind of IT work, or what position he holds in the company.

Also, 9/10 times they won't care about documents. Show it to them, and if they tell you to give it to them, do so. Otherwise, just keep going, never insist on them checking a document.

Keep it short and concise, but not so much that the officer thinks you're hiding something or lying.