Civitai is pretty messy and having your images in the correct order is a headache. Here is a tip to achieve that.
The easiest method is as follows:
Submit only your first image.
Clic on your entry then clic on the Edit button.
Add your second image, then submit your entry.
Edit your entry again.
Add the third image, then submit your entry again.
Repeat.
It is tedious, but it works.
If you want to try to save time (no guarantee), you can try this:
Post all your images.
Edit your entry.
Refresh the page to see the current order.
Remove everything before your first image.
Look at the remaining images. Remove every images that breaks the correct order, keep the longest correct sequence starting from image 1, and remove everything else. (For example, if you have the order 4, 1, 5, 6, 3, 7, 2, 8, the longest sequence you can make is just 1, 2. All the others should be removed).
Add back all the images you just removed, then submit your entry.
Edit your entry again.
Refresh the page to see the current order.
Now, you will at least have the previous sequence in the correct order. Once again, remove every image that breaks the sequence. (For example, if you now have images 1, 2, 5, 3, 4, 6, 7, 8, you have to remove image 5 to get 1, 2, 3, 4. You must remove the rest because the next one should be image 5, but you just had to remove it).
Add the removed images again, then submit.
Repeat the edit, refresh, and replace process until everything is in the correct order.
With a bit of luck, you can have 8+ images in the correct order with only 3–4 edits.