I've never been on a spin bike that measures speed. Wattage, yes, but not speed. I'd ignore your instructor regardless. Everyone, from beginner to advanced, should get THEIR best workout, using the instructor's suggestions as just that. Suggestions. Set your pace and resistance to your abilties and goals. Your instructor ideally shouldn't establish one "speed"--whatever that even means on a spin bike--for the entire class.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher