When the time comes for the real performance, she puts on a good show and the audience applauds. However, she and Johnny know that she missed several steps. The most difficult maneuver she is trying to learn involves a leap into the air in which Johnny catches her and holds her prone high above his head. Before the audience, she misses her step and falls into his arms. She just continues to dance as though nothing is wrong.
Nobody seems to notice.
However, later in the movie, in their triumphant final dance, she finally does it. She leaps into the air and Johnny raises her over his head triumphantly. One wonders if it is really possible for a rank beginner at dance to become a world class dancer after just two weeks of intensive instruction. However, that is only the most obvious plot. Getting back to Penny's medical emergency, the medical emergency is that she needs an abortion.