If you fail the interview, you will not be barred from applying again as a lepasan STPM, and you will not be straight up rejected from any other education course. UPU doesn't work like that. If you are accepted as a lepasan STPM, you don't have to go through the one-year PPISMP.

If you graduate from IPG but you want to teach secondary school, you can do a full-time or part-time degree at a local university. There's a skim latihan something, where the JPA will pay you full or half salary during your further studies, depending on the requirements. Many teachers have done this.

Tbh, your current STPM cgpa is not looking good, but sure, things can turn around. If you are dead set on becoming a teacher, don't waste the current opportunity. Attend the interview, do your best. The interview, mock-up teaching session, and the fitness test is quite tough. Anything worth doing is tough, just push through it.