@KodaiWand welcome to the forum.
If you are on a keto diet, your body is not used to dealing with a quantity of carbs, irrespective of whether you are a diagnosed diabetic or not. Before having a OGTT it is important to eat carbs for a number of days, so that your body is ready to deal with the glucose, otherwise, as you have seen, you will "fail".
What had you eaten before you had the large spikes of up to 12mmol/l? Was this the effect of a sudden input of carbs, which your body wasn't expecting?
What do you eat? What are your normal meals? Perhaps you are unwittingly eating something with hidden sugars.
Sally