I Don't Want to Become Crown Princess!! Series by Saki Tsukigami, Natsu Kuroki

Liddy, who was Japanese in her previous life, is now the daughter of a duke and engaged to marry the gorgeous Crown Prince Friedrich. Sounds like a dream come true -- except this is a world that practices polygamy, and Liddy refuses to marry a man with multiple wives. To sabotage the engagement, she loses her virginity to a stranger, but that plan is thwarted by a surprising revelation. What will happen to Liddy next in this hot fantasy romance?

To escape her engagement to the Crown Prince, Liddy decides she has no choice but to lose her virginity, and fast! But in her haste, she makes a terrible mistake. It turns out the man she slept with at the Masquerade Ball is none other than the prince himself! Not only that, but he's left his mark on her, literally, and it's impossible to erase. Just how will Liddy get out of this mess?