Is it bad if you make yourself vomit?

Generally, yes. Self-induced vomiting is generally not a good idea: it deprives your body of the nutrition contained in the food you throw up; acid from stomach can erode enamel off teeth, leading to tooth decay. Violent vomiting can damage the esophagus resulting in tears & possibly bleeding, which may need surgery to repair. Repeated self-induced emesis may be a symptom of an eating disorder.