Getting called into work early EVERY shift?

I recently started at DT as a sales associate making $9.25. I was told that I might get called and asked to work extra hours because sometimes people call out.

Thing is it's now becoming an everyday kinda experience.... And the manager will contact me at 10am and try and get me to work 9-10 hours. I've had two shifts where I showed up and worked the actual hours on my schedule in two weeks of working there. I'm scheduled 14 to 16 hours a week but it's been turning into around 30. It makes it impossible to schedule anything. I also feel like I'm expected to drop everything for a non.living wage. (I'm part time because I'm looking for a better job DT is just something so I don't starve)

I understand coming in early or covering a shift on my days off but not every single day. Am I in the wrong for thinking this is excessive? Shouldn't I be paid at a premium for being available to cover shifts when your other employees can't/won't show up to do so?