Hi, @Mathaneshan1998! I hope it isn't too late to reply. First of all, congratulations for achieving CGPA 4.0! Technically, you cannot pursue your studies in public universities as you are not qualified to apply for undergraduate placement through UPU. However, you can try to personally contact the administrator of your choice of public university and apply directly to them. I personally think there may be chances your application will be taken into consideration concerning the fact that your academic pointer is merely excellent. You should contact them ASAP because the UPU result will be announced on 1st August.
If let's say your application is declined and you still have to enrol in the private institution, I suggest you search any available scholarships outside from the university itself. There are many scholarships provided for chemical engineering students like you such as Shell, Yayasan Khazanah, etc. Nonetheless, most scholarships for undergraduate students usually require your first/latest semester result of your undergraduate programme AND your foundation result. It doesn't hurt to struggle financially for the first semester if you are willing to take risks and committed to hunting for scholarships. PTPTN should be the last choice to be taken into your main concern.
Good luck and may the Force be with you.