No one here can tell you if it will worsen or not. Knowing it was this way when you bought the phone however, indicates it won't likely go away. Keep an eye on it and if it gets worse, schedule an appointment at your Apple Store Genius Bar or Apple Authorized Service Provider for screen replacement options. Do NOT let an iFixit, 3rd party type service replace the screen on your phone, even if it is appreciably less expensive. They do NOT have access to authentic Apple screens and certain features may be made inoperable with an aftermarket screen. Plus Apple will not touch a device, which has been tampered with in the future.