When you place a reference to a field from a related table directly on your layout, such as is done with your merge fields here, the relationship references the "first" related record. That will be the oldest related record unless you use a sorted relationship to make some other related record the "first" such record. To specify a sort order for related records, open Manage | Database | relationships and find the relationship line linking your layout's Tutorial: What are Table Occurrences? to the table occurrence named "gifts". Double click that line and you'll see a button for specifying a sort order for Gifts.
Here are two sort orders that you might specify to get the results that you want:
Option 1: IF you have a date field in the gifts table, select that field for your sort order and sort the records in descending order.
Option 2: If there is an auto-entered serial number field in gifts, you can sort in descending order on that field.
The only difference between the two options is if you get two gifts records for the same donor with the same date, the first option may not show the most recent gift but the second option will.