OP is attending college and will thus be a transfer applicant. Depending on what s/he means (Ivy league only? Top 25 universities and LACs? State Flagships?), “prestigious schools” may not admit transfers at all, or only a handful doing a “lateral” transfer (ie., from a top US college to another). In addition, the 27 on the IB WILL count and WILL NOT be totally offset by APs (where OP is hoping to get 5s).
OP, can you retake the IB exams/subjects that you bombed?
Finally, for top schools, extra curricular activities take primary importance. Make sure to stay involved in the activities you did in secondary school, and show a higher level of responsibility, leadership, and achievement than you did as a high school student.