When you run an API request, Data Fetcher transforms the response into Airtable records using the response data transformation and response field mapping. Sometimes this will produce more records than you want, e.g. if there are nested array items in the response. You can limit how many records are output by setting the Max response records.
On the create request screen, click to open the advanced options.
Scroll down to Max response records.
Enter the maximum number of records.