Will all injected insulin eventually absorb or can some part of it just dissappear without any effect?

I am wondering this because I earlier injected 4 units for my, quite fatty, meal and soon after my bs skyrocketed as if i hadn't injected any insulin at all. As i knew that I had probably injected into an area with slow absorption I decided to wait a bit, but my sugars remained high. I then later injected an additional 2 units into a different area and that brought my sugars down into acceptable territory.

Now I'm just worried that the insulin I injected earlier is just lurking somewhere and that it will suddenly absorb when i move about. Is my fear justified? Or is it more likely that the insulin absorbed but my bs just went up for some other reason?