My move got skipped

Ok so i was trying to level up my pokemon and all of a sudden my wartortle gets to lvl 20 and wants to learn rapid spin. So i think ok great but of course it skips it and now i didint learn the move im still mad at this and would be so happy to the point i would even vote on this server and tell others too if i could get the move back anyways thanks for reading this

 

Wartortle learns rapid spin at level 21. Try leveling wartortle again and check