Shoul I ask for a raise?

I work at a program with autistic adults. I been there for 8 months now and starting the pay was $18 and hour and it’s only 6 hours a day and 6 days. I used to be a 1:1 with this girl so my job was only to be with her ( she neee a lot of assistance and is not very active etc) well one of my co workers quit and I took her spot of making lavender products so I basically moved up to being a 3:1 which Means I work with more people at a time now, I have more responsibilities and it’s more stress too because I’m in charge of more.

I don’t think it’s fair to have the same wage as my co workers who when they don’t have anything to do they just hang around and I’m busy all day.

Is it too soon to ask ? What should I do?