Yes, the eye shape is heredity which is decided by gene. However if you want to change the shape of the eye to make it perfect to match with your clothes and other things, you could choose to wear the contact lenses to make them look round and big. You could also choose the favorite color to make your eyes look beautiful.
I can see you are very curious about the truth. So, according to some medical research, eye shape, as well as eye color and the length of eyelashes, could be hereditary because of the genes. And your assumption is just about right. But exceptional cases could be seen from time to time. Anyway, gene plays the most important part in deciding what your eyes will look like. Just take care of your eyes.