My question is how can you pay your bills on 20 hours? LOL.
My guess is that they have part-time compatible bills. My daughter is a college student. Her "expenses" are gas for her (our) car, her Netflix subscription, her college "incidentals" and entertainment/eating out. She has expenses, but she's not trying to run a whole household on her earnings.
My daughter has worked at the same family-owned pizza place since she was 15. She loves the people there and doesn't mind the work. She worked through high school and when she left for college she had an open invitation to come back for summer/school breaks, etc.
The summer before she left for college they were scheduling her almost 40 hours a week (more than she really wanted to work). She expected nearly the same the summer between her freshman and sophomore years, but she was lucky to get scheduled for 12. The issue was two-fold: 1) they had staffed up for summer assuming that some of the new hires wouldn't last, but they all did. 2) Since food prices were skyrocketing, they were trying to minimize labor costs, so they didn't have to raise prices. While a "full staff" might be 12 employees, they were working with fewer, especially during the week on less busy days.
She did OK by picking offering to pickup extra shifts/call-offs, etc and by cross-training on every station so she could pick up any shift.
This summer, she has gotten a second job (one that's more related to her intended field.) That one's 20 hours/week... and she's getting about 30 at the pizza shop. Plus she's taking a summer class so she is one busy girl!
So my suggestions would be:
1) ask if you can get more hours
2) if there are no hours available for bagger/cart guy, can you cross train to get hours as a stocker, cashier or bakery clerk?
3) Look into getting a second job somewhere else.