I think Reg might be right, if you haven't included Malt in your mini mash it wont have converted the starch. good rule of thumb is that you need about 60% base malt (ale/pilsner) as a minimum.
The fact that you are missing the gravity you would have expected from the Oats is a pretty fair indication that it wasn't converted and thereby made soluble, as "gravity" is measuring what's in solution.
With unmalted Oats, given that they are rolled/flaked, you will have a lot of Glucan and Starch available.
To get the most out of say 500g of oats, mix it with say 750-1000g of milled ale/pilsner malt with around 4Lof tap water at tap temperature in a pot (with a bit of room).
Put on the stove top, set to low (lowest).
Allow to warm slowly from ambient to say 80oC, stir occasionally (the ideal rate of rise would be 0.5oC/minute). This will take you through all the enzyme activity temperatures, most importantly in this case, through the Glucanase, Protease, and both Amylase temperatures, in the process converting most of the oats into a soluble form.
Pour through a strainer lined with some fabric (tea-towel chux…) boil the extract for at least 10 minutes, you could do a mini sparge which might get you a bit more extract, but personally I couldn't be arsed.
The boiled wort can be your makeup water for the rest of your ingredients (kit, LME...)
Mark
