I learned that chemotherapy makes it worse when you have sarcoma cancer. is that true?

No. : Sarcomas of bone (osteosarcoma, ewing's etc..) are almost incurable without chemotherapy and have a very good chance of cure with chemotherapy. It is not clear if chemotherapy helps for soft tissue sarcomas, though. In some studies it helps, in others it doesn't, but it certainly doesn't make things worse. Each situation is different, so ask your oncologist.