You can also get lumps from injecting at the same site too many times.. keep changing sites every three days you should be good.
if you get a bump after an insulin injection it means that you chose a poor injection site. Insulin absorbs into subcutaneous fat. So wherever you shot and a bump comes up, that means there was not enough fat in that spot to absorb the insulin you just shot.
try picking a more fatty area and shooting very slowly.