You didnt get a small clear container with a lid with that kit?
10-15 mls should work for you.
Usually a small vial or tube comes with a clear water pH test kit. Mine says fill half way, like 15 mls or less then add drops and give it a shake.
A cover is needed! If no cover just let it sit a minute or two. If you use your finger to cover it then mix your pH drops and the water, the sweat and oils on your finger tip will give you a false reading!