My name is Lilith, I'm on the Social Care team at Shopify.
It sounds like you may have more images than there are variants. I've got a screenshot of my test store below so you can see what I mean.
In my product page I have 3 variants and 4 images:
In my CSV you can see the 3 variants and an extra line that has its image link and no other variant type details:
Now as you scroll further to the right on your CSV in spreadsheet mode you can see that the only item that is in that row is the link to the stored image that belongs on that product page:
From your described situation, it seems likely that you may have 3 images on your product page.
Let me know how you do with the information above! I'm happy to answer any questions you think of as you work on your business.