Hi, and welcome to UK Fungi.
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These look small? - but photos can be deceiving - exactly how tall are they?
You mention propagation fabric, which suggests that they may be in a greenhouse? - If so, is it a heated greenhouse?
They have the looks of a very small "Inkcap" species.
One of which is often found in plant pots (it has the common name of "plantpot dapperling" - Leucocoprinus birnbaumii
However, that species is usually more of a sulphur yellow colour, but I understand it does occasionally appear in a paler creamy colour.
It is generally very short lived (i.e. maturing and withering within hours)
Your mushrooms may be that, or something similar.
A close up shot showing a fully mature, open capped example, along with a similar shot showing the gills. would be good.