Please someone should answer this. Am loosing 5k already

Why is the balance higher than actual

if I tell you, will you give me the 5k?

This is the reason the balance is higher than you are thinking it should be.

You had 30 naira remaining from your 50 naira after spending 20 naira. Then instead of spending more from the 30 naira you added 21 naira to it making your new balance 51 naira. You stopped spending at 30 naira then decided to earn more money(that's what happened when you added the entire balance column in the paper).

On the other hand, if you want your balance to be equal to the original money you had(50) just add the first money spent (20) to the remaining balance (30) or add the entire spent column.