IMO that shelf is really too shallow to hold much you might be a ble to get e apiece to glue onto the back of the shelf to give you the right depth and not be obviuos

are you storing your detergent on that? those jugs are heavy. you need some very strong brackets that are drilled into the studs t hold the weight. Hopefully that's what you've done.

as for the wood, again, what are you going to put on top of it? if everything fits, I don't think it's a big deal. I'd rather have the shelf a bit too large than small tho.

do you plan on doing anything to wall behind it to jazz it up a bit? you have the perfect spot to do something

It's a laundry, functional is what's important. Are the supports strong enough to hold the weight and is the shelf high up enough to clean behind the units and to access the dryer vent for cleaning?

Can you reverse the brackets? I.e. longer side fixed the the wall, or studs if it is just plasterboard.

I think Nick just figured it out.