SQLite database to data class

I want to create an application.
My app is a book and I created a SQLite database for my data as "mybook.db" that is 3.5 MB in size.
I tested my app and all activity works good!
Now I want to publish it on the Play store.

I used In App Billing for selling my content to premium users, but I realized that my database is available on "./data/data/myapp/database" and also in the asset folder of apk package, and anyone can copy and use it! :(

Now what I can do to save my data?
is it possible to convert sqlite to android class?
is it possible to encode data?
How I can save relation between may data?

Please help me...

----------- Edit ------------ i don't want use SQLCipher !

is there any way to use another data structure for saving data?