It is normal that you are going to feel a bit tongue-tied whenever you are with your crush. There will be moments when you will feel tongue-tied especially if you are asked a question. No matter how many times you practice, you will still feel a bit a bit anxious.
You should try to remember that your crush is just a person that is asking you something or is just having a conversation with you. Now is not the right time for you to think of things that will impress your crush. What you can do now is just provide the information that your crush needs. It might make you more memorable.