B500A1 re-assembly help please!

[Quebec]

Hi all,

For an unbeknown reason I decided I'd strip my B500A1 (cheap abs aeg, mounded plastic no seperatable receiver or takedown/pivot pins). My dad got it for me for my birthday and although I know they're not meant to come apart I carried on regardless.

It's my first airsoft gun for a few years as I used to play with friends in our gardens a couple of years ago, so I have some very limited knowledge.

On dissasembly, the hop up unit an the black shroud around it (I'll attach pictures) popped off so I had to make an educated guess as to the orientation of it when I put it back in. The charging handle was easy enough, the fake forward assist button I left in place but everything else came out including the motor and gearbox and ejection port cover, all rails etc.

Everything went back together okay apart from the above hop up/barrel/shroud assembly, but I couldn't get the two halves to shut as it was fouling on the hop up/shroud assembly somewhere and it's beaten me.

Images attached, does everything look correct and is it ok for the small tapered seal next to the spring on the barrel to push in to the hop up unit?

Also, the square metal plate with a threaded hole - I have no idea where this sits?

The small black plastic piece - I believe it sits in the magazine well next to tge barrel but can't see a place for it.

Sorry for the huge post and thanks in advance.