1240 w by 1754 h with exceeds the size of the iPad screen this might be a problem depending on how iBooks displays the ePub file.

Three test files attached

1. Original file stripped of all but the cover and 1st chapter saved with Sigil
2. Original cover replaced with an image smaller than the screen of the iPad
3. Same 2nd file but with width="100%" remove from the IMG tag

Let's see if any of these work better than the original.