The beta is specifically used as a test to show the development team how much strain the server's can take and what powers/weapons/vehicles need to be buffed or nerfed in order to make the game better. It's not a final product and not a way to get a leg up on other players before the game launches. If it was an early access such as Battlefield Premium has for it's members then it would transfer over. It is not however, so unfortunately the items you earned will not be transferred. I can understand the feelings you have right now but don't worry. You can earn way better items when the game launches in september.