The most helpful tool to stay calm, focused and confident is your BREATH!
Simply become aware of your breath and keep it even (or try to keep it even)
If you have a minute or two, do a simle Meditation: Become aware how air is passing through your nostrils. With Inhale cool air is passing in throug your nostrils. With Exhale warm air is passing out through your nostrils. Just keep your focus on this subtle sensation inside your nose. Close your eyes. Leave all the worries…