Question : is receiving chemotherapy treatment in a large open room with other patients present impinging on my hipaa rights?

No

Fr Chuck is right.
I just completed a required HIPPA refresher. HIPPA covers unauthorized disclosure of your information.

Yes, Hippa has more to do with your physcial records, and the staff telling others what they read or heard. Just as in the treatment room, you are in a waiting room, they call your name to go back, merely the fact you are going to the doctor because someone sees you there is not part of it.

If your nurse tells someone at 7/11 you are getting a treatment, it is,

No, there is no infringement on your HIPPA rights. Unless, as Fr Chuck said, you hear from someone who heard from someone who was listening to someone talk about you and your treatment. But that someone who blabbed in the first place - if that person was your neighbor, you cannot help that much - if that someone was the nurse or a lab tech, etc. then you have grounds to file a complaint.