Were you hired in the category of temp? My daughter works at a hospital for a 16 to 24 hour position and ends up working more hours than that at times because because her status as temp doesn't have specific hours listed for her. She is to fill in as needed.
I think the facility has the right to use you for any numbers of hours that they need you. You have the right to say you can't work that many hours. I urge you to talk with the Director in a calm and reasonable way, expressing your wish to be a part of the team and to be helpful while at the same time this many hours isn't working for you. Ask how this situation could be managed so that it's helpful for both you and your employer.
Do not try to turn this into a "this is unfair" sort of fight. It's not about right or wrong. It's about you working the number of hours you want to work. If they need someone more full time then it may be that you'll have to quit. I suggest the need has grown and it's time for a discussion.
It's also reasonable, if you choose to stay and work more hours, to ask that the position be reclassified so that you will receive benefits. In Oregon you have to consistently work 32 hours, I think, before it's considered full time and has benefits.
Just go to the Director and discuss this with her. Do not make it a right or wrong conversation. It sounds like you have difficulty being assertive and your fall back mode is a need to show that the other person is at fault. That rarely gets any one what they want.