Lovely and a happy print! You could make drapes from the flat sheets shown with it. Line them and use a roller blind to make it darker. I think you need a small print to go with it.

Go bold and pick up on the fuschia? Use some check or plaid for a little 'snap'.

I would pull the darker green out of that to tone it down a little.

A darker more sophisticated color like navy or dark green would help mature the pattern. I'd skip the accent wall and paint all of the walls the bold color.

Yes! I agree with Linda - that green didnt even register with me at first. But I would still bring in some graphic pattern for punch.

The darker olive-like green would help the space look more mature.

But maybe reconsider the bedding? I know you say you love it, but if you got throw pillows with that cover, or similar artwork instead, you'd have the feeling, but less of it.
It looks ok, but is bold. Have you tried it in your actual room? How big is the room?

Does your photo show the bedding that you are using? Can we see your whole room?

Here is a color snap from SW, you have your choices

Celery girl, how do you do that? Thats very cool.

I might pick a goldy brown/beige from the duvet/comforter or a soft green.

https://www.sherwin-williams.com/homeowners/color/find-and-explore-colors/paint-colors-by-family/SW6127-ivoire#/6127/?s=coordinatingColors&p=PS0

https://www.sherwin-williams.com/homeowners/color/find-and-explore-colors/paint-colors-by-family/SW9028-dusted-olive#/9028/?s=coordinatingColors&p=PS0

That sage green wall color and pale blue sheet look amazing with the floral!

I would pick up that dark Hunter Green from the duvet to paint the all walls, then perhaps get solid velvet curtain panels in the dark fuschia or the lemon/gold. Have the duvet be the only burst of pattern, but bring in some neutral textures, like perhaps a painted bench with a cane seat, and nightstands with textured linen look. I think if you ground this in jewel tones and textures, it will be more dramatic and less teen-like. Some brass lighting or accessories accents would also be beautiful.

Some directional ideas, but use your colors from the duvet:

Morning Glory by SW