Two units a day shouldn't cause much of any fat at all, that is really not that much (your pancreas, if working normally produces about 40 units a day itself) so that extra couple is unlikely to be "noticed" much

But generally insulin use can cause "body fat" (not specifically in the belly)

Body fat is created by extra insulin and excess carbs that are not needed for energy. They are converted to body fat and stored away for when they are needed

Unfortunately most of us never seem to "need" that store fat and it hangs around 😁