Spells that were cast before Razzle-Dazzler entered the battlefield count. If Razzle-Dazzler was the first spell you cast this turn, the next spell you cast this turn is your second spell.

Once Razzle-Dazzler has been blocked, casting your second spell for the turn won’t remove the blocking creature from combat or cause Razzle-Dazzler to become unblocked.