Emma Carlson-Berne 
Running Scared [PDF ebook] 

Olivia likes running — when she’s doing it for fun, that is. But when her friend convinces her to join the track team, Olivia panics. She’s convinced she’ll come last, and people will make fun of her. So Olivia starts dropping out in the middle of her races. When her aunt realises what she’s doing, Olivia has to face her fears and quit running scared.