You're Mine Free Novel by Penny Brooks

Harper is feeling self-conscious in a revealing bikini at a pool party hosted by her twin brother, Ryan, while their parents are away. Her best friend, Sadie, is determined to boost her confidence and get her to join the party, despite Harper’s insecurities.
The event is filled with classmates, music, and drinks, and Harper feels overshadowed by her brother’s popularity. However, when she notices Easton, the most popular guy at school, her interest piques.
Easton, though seemingly indifferent, can’t help but notice Harper in her bikini, sparking an unexpected tension. Amidst the party chaos, their paths might just cross, leading to surprising developments.