Look up sum in help. It doesn't work like you think. A summary field, however, can return the total that you need.
The use of numbered fields is a big red flag and a source of your reporting problems.
It is a data structure (design) problem.
These fields should instead be separate records, in a related table and there should just be one field for amount; and one for date paid.
Plus, most likely, a description field.
What does Amount1 represent? What does Amount2 represent?