Instructors want their students to be confident, especially in front of patients. However, if you are unsure of a med you're giving or a skill you're doing always clarify with your instructor or nurse about it. People's lives are in our hands! You don't want to pretend you know what you're doing when you don't. That's going to lead to a mistake and could hurt/kill a patient.
At the same time, if you act nervous in front of a patient they are going to be way more scared about the procedure. When you know what you are doing, but you are feeling nervous - this is when you can fake it. Sometimes I'll clarify in front of the patient by confidently asking my instructor something like, "We give this injection by pinching the skin, right?" This verifies that I'm doing it correctly and also shows the patient that I care about their safety. But this will backfire if you ask and the method you state is incorrect, so make sure you know your skills. :) If you completely forget how to do something ask your instructor about it before you go into the patient's room.