Data in FY20 and FY21 is also populating because you have entered 0.05 in the formula bar of unit cost% line item. Doing this populates each cell of that line item with the value entered in the formula bar.
To populate just FY19, first clear the formula bar and then click on FY19 cell of unit cost% and enter 5 there, in this way it will only populate FY19 cell only.
And, to enter 5% in the cell, you just have to write 5.
When you enter the numeric value in the formula bar it converts it to the %, hence 5 become 500%, but when you enter the values in the individual cells it keeps it as % so if you enter 5 in a particular cell it will accept it as 5%.
Try doing it yourself.
NOTE: You want 5% in FY19 cell only, but you are entering the value in the formula bar, instead enter the value in the cell under FY19 of unit cost% line item.