It's hard to understand what happened to Cain. This word "under" is either cursed "FROM the ground," or "OUT OF the ground," or "MORE THAN the ground," or "ON ACCOUNT of the ground," etc., etc.
Cain may be cursed (like the serpent), or the ground is further cursed (like w/ Adam). It's difficult to determine.
Now you are under a curse and driven from the ground, which opened its mouth to receive your brother’s blood from your hand.
Genesis 4:11 (NIV)
from, out of, on account of, off, on the side of, since, above, than, so that not, more than
from (expressing separation), off, on the side of
H4480: מִן (min)