[dice]

[mushroom in picture]

I would definitely pull and toss that. It looks like an amanita
pantherina, an exceptionally toxic mushroom. Not something
that you want anyone to eat by mistake.

I have not seen any odd mushroom types come up in pots that
I have inoculated with MycoGrow Soluble. Which exact
MycoGrow product did you get? (They have a few different
mixes of spores that they sell.) It should say on the label on
the bag.

Edit:

(Amanita pantherina is not something that I would expect MycoGrow
to have around, even though it grows wild in the Pacific Northwest.
It is not an edible mushroom, not medicinal, and not a mycorrhizal
species. It would be about as welcome around a commercial spore
production facility as poison ivy, and it is distinctive enough looking
that it would be hard to miss if it were mixed in with other mushrooms
that were being grown for spores.)