I took out a 13,000 EGP loan, based upon my income, from the Bank of Alexandria. The bank deducts a monthly sum of 100 EGP from my salary. After calculating the interest, I found that upon the date of maturity, the repaid sum will more or less be 18,500 EGP. The reason I took out the loan was to build a concrete ceiling for the second floor of my house, and a third floor, fearing future rising prices. What am I to do now after I have spent the money on constructing the ceiling and the third floor? If this is considered usury, how can I repent from this sin since I do not have the money to pay back the loan at present?

The legal axiom states, "Every loan that incurs benefit is usury". This transaction is considered usurious and is therefore an enormity.  You must repent by regretting having done this sin, resolving never to commit it again, and doing rewardable deeds in abundance because Allah Almighty says,

Allah the Almighty knows best.