iPhone 7 screen very sensitive

I have an iPhone 7 I bought off eBay and while it works okay, the screen is over-sensitive.

So

• Long press turns into 3D touch
• Very hard to do a normal "long press", for example when wanting to uninstall an app
• Sliding from the left to go back a screen turns into the 3D touch to bring up the task switcher

I've adjusted the 3D touch sensitivity to firm which has helped but not solved it.

The left side of the screen is coming away from the case slightly but not enough to notice.

As it's out of warranty and I'm relatively confident in repairing myself, any ideas what the solution to this might be, or will I just have to get used to it being careful?