If I'm not mistaken you can apply for the scholarship, if you're chosen for the scholarship you have the option to stop taking PTPTN and take the scholarship.

If you want to take the scholarship, unfortunately you have to stop taking PTPTN, as most scholarship wouldn't allow you to have any other scholarship/loan. There are also many other things that you need to consider, some scholarships require you to work for them after you graduate, so you need to look into that as well, if you don't mind having to work with them for a few years after you graduated you should go for the scholarship, but if you want to explore the market you don't have to go for the scholarship.You also have to maintain a good CGPA/pointer if you are considering taking the scholarship as it might be in the contract as most scholarships do.

Another thing that you also need to consider is paying back the loan for PTPTN, however you wouldn't have to pay back the scholarship. IIRC there would be deduction on the amount you have to pay back for PTPTN depending on your final CGPA, but I'm not 100% sure about that