First time growing indoors [contamination]

I set up an outdoor mushroom garden last year, but that just ended up being a slug farm…

I’ve finally made some space in the basement for indoor growing, and am curious if this is mycelium or a contamination, before I set up a second tub.

This is 5 days in using shiitake grain spawn (purchased) with oak sawdust and wheat bran. I pressure cooked the substrate, disinfected all surfaces with 70% alcohol, and wore gloves and a mask throughout the process. It’s been stable at 99% humidity and ~65 degrees F.

Thanks I advance!