Francia Raisa continued her birthday celebrations Sunday in Malibu, showing off her curves -- and her scars from the kidney she donated to Selena -- as she played volleyball with friends.

It was another scorching hot summer weekend in the 'Bu, and Francia made it hotter ... leaving little to the imagination in a skimpy swimsuit that matched her sunglasses and hair.

Francia showed off her athleticism ... serving some aces and bouncing around in the sand.

The beach day capped off Francia's birthday week, which included an olive branch of sorts from Selena, who wished her well with a social media post after their recent falling out.

As we reported ... in the wake of Selena's birthday message, Francia followed her back on social media and told paparazzi there's no more beef between them.

Now that Francia's following Selena on Instagram, she's probably seen Selena's weekend thirst traps she posted from a boat ride.