What should I do to repent to Allah the Almighty after taking out a loan of 2800 Dinars from a usurious bank and paying off part of it, and regretting that, knowing that I can pay the remaining amount in a single payment?

What you have done is cooperation in sin, transgression, and usury, because by doing so you act as an agent of usury for others, as usury is the excess amount beyond the principal that you will pay them. You must return the same amount you took from them without any increase, and they are not allowed to demand an increase. If they compel you to pay it, then give it to them. It is advisable to pay the remaining amount in a single lump sum to be rid of this matter.