Remove gray area outside graphic?

[Pacer]

Sorry this is probably covered somewhere but I don't know the tech terms for how to search for it or even how to ask...trying to create a social media post using a Facebook template inside Pixelmator Pro. I picked a template inside PP and deleted the layers, etc so it was basically just a blank canvas from what I could see. Then I imported my graphic into it, which is all ready to go....what I want to do is take the assembled image and "Export for Web" -- but without the extra border crud around the sides of the image...I'd like to post to socials and just see the image with its nice, rounded corners and not a big gray square around it, and/or weird breaks, etc.

I tried Image -->Trim Canvas -->Transparent Pixels and it still exports with a weird square around it. Help? Sorry for dumb question. I inserted screen shots below to show the progression and current errant end result....thank you kindly for what has to be a simple fix that I'm too dense to figure out!

PP image assembled:


end result:

[mccoytest]

Did you crop the result to the desired limits ("c") wherever you post mya not show your nice rounded corners.