11.4 update on SE, Screen is playing up

Hi, updated my SE and now my screen is playing up. It prsses random keys when typing a message and also jumps on apps.

Has anyone else had this? I'm not sure if it is the update or a faulty handset? The phone is only 18 months old, but apple warranty is only 1 year ! So annoying. Still paying for this phone on contract and its not working.