This is related to the export to GeoTiff. When exporting to GeoTiff the scaling information is not considered. So you get the raw data in GeoTiff.
So you need to scale the value first to the geophysical representation: for TSM it is like this:
value = 10^(raw * scalingFactor + scalingOffset)
You can see the scaling values in the information dialog:
If you only want to export TSM, it should easily be possible to add the BandMaths operator to the graph.
You can do after the Resample operator. As expression just use the band name TSM_NN. In the new band, the scaling values are already applied and if you export this band you should have the correct values.