I Became the Dying Female Lead's Sister

In a twist of fate, a girl wakes up as Lynzelle, twin to her favorite novel's dying female lead, Lykke. To secure Lykke's happiness, she volunteers to wed the fearsome prince, Hernan, in her sister's stead. But hold on... The scary prince turns out to be super cute, sparking unforeseen feelings! Everything seems perfect until Lynzelle's health...