I agreed to work part time not full time.

I started my new job recently, I told them I wanted to work part time, manager asked if I was okay with working 24 hrs per week I agreed, I take a look at my schedule and they have me in for 32 hours. 4, 8 hr shifts. I’m in Canada, anything that’s 30+ hours is considered Full time.
Should I talk to the manager and ask why I’m being scheduled for 32 hours instead of 24 hours? How do I approach this, I don’t want them thinking I’m unreliable or nagging them.