Answer:
There might be confusion between the mistaken identity of the twins. This might cause problems with the disguise of Viola. People might find out who she is. Olivia marries Sebastian, thinking it is Cesario and this further complicates the already complicated love triangle between Olivia, Orsino, and Cesario.
Step-by-step explanation:
Also, the answer above is copied from PLATO. If you use it, tweak it a little bit to avoid getting it wrong.