I think your field names are incorrect. Perhaps you could post a screenshot of the field group edit page so I can see the repeater / sub fields
Also, a screenshot of the edit page would be good.
As for the 75 sub fields, this is most likely due to 1 of 2 things:
1. You have selected a minimum of 75 rows for the repeater field
2. You have a previously saved value with the same field_name. This would have saved the value 75 at some point
Welcome to the Advanced Custom Fields community forum.
Browse through ideas, snippets of code, questions and answers between fellow ACF users