General interview tips:
Don't be afraid to admit you don't know the answer.
Feel free to ask them to clarify a question - even if you think you have the answer, while they are re-asking, you have time to really consider the question and put together a good answer.
Don't waffle or lie to fill airtime
Ask as many questions as you can
Don't expect to spend time talking about the stuff you are confident in. If they are a good interviewer, they will quickly determine whether you understand a particular subject and move on to something that is a bit less certain. No point in wasting time exploring stuff you clearly know.
If you think you gave perfect answers to every question, you probably didn't get the job - you should leave a time-boxed interview exhausted but frustrated that you didn't say everything you wanted. So, if you think you failed and keep on thinking about stuff you should have said, consider it a good thing!
Good luck!!