How can I tilt an object to fit onto a shelf?

Hi all,

I'm working with a kit to create a close mockup of a wall/desk scene. Since nothing had all the objects I needed, I'm having to add outside objects to the shelves, such as the coffee cup pictured. Since the perspective/camera angle is wrong, I need to tilt the object back so it'll sit realistically on the shelf.  Since several other outside objects will also need to sit on shelves, I gotta figure this out.  Although I'm not new to Photoshop, I haven't really delved into the 3d portions until now, and I'm suddenly feeling like a beginner.  I've spent pretty much all yesterday afternoon and evening researching, watching videos, and trying everything I can find...and failed each time. 

It seems like this should be a simple task and I'm missing something obvious--but what?  I've tried vp, perspective warp, 3d, and skewing. But since I'm trying to tilt this back, not skew it to a side wall or anything, I can't get it to work. At one point I had it in 3d and was moving it around with the camera, but the end result was just really really bad.  

Could someone clue me in? I'd really appreciate any thoughts or ideas anyone has.  Attached is a sample file to show you what I'm attempting to do.  

Oh, and I'm running PS 22.0.1 on a Surface Studio with Windows 10.

Thanks for your time!