As an international undergraduate student with bad secondary school?
Im not sure what country you live in, but you might be able to retake your High School / GED exams and improve your scores before you apply. Why not try that option? Sometimes, good students end up with poor scores for various reasons - family issues, health, relationship issues etc can all have a bearing upon examination performance. If you have the option of retaking your exams, then maybe you might consider that option? Best wishes!