Have your cake and eat it too.

The correct phrase here is that "you cannot have your cake and eat it, too".

The expression, 'You can't have your cake and eat it too.' means that if you want to eat your cake, you will no longer have it. It's usually used to admonish someone who is fretting because they can't have everything they want.

yes, but you can't eat it too.

If you have half of something and you eat that half you have none; don't forget, "You can't have your cake and eat it too."