You may be able to resolve this issue by adjusting the margins on your book here, if you have the Custom theme enabled
https://leanpub.com/YOUR_BOOK/settings/theme
...making sure you replace YOUR_BOOK with your book's unique web address.
The relevant options you can adjust are Inner Margin, Outer Margin, Top Margin, and Bottom Margin.
We'd also recommend that you try searching or posting about this on our Authors Forum here:
There's a wealth of (hard-earned!) experience that our author community has developed over the years, and people are often willing to share what they've learned about e.g. getting their books into print.