Jen, or
Jenny. I know a
Janet who is known as
Jan, and spells it Jann: everyone except her loving husband thinks it looks silly, but she just wants to be different.
Now I'm thinking about
Jenny and
Jen, but also
Betty and
Bet, Bett or
Bette. I'd avoid
Bet if I was a
Betty because it's a dictionary word, but that doesn't apply to
Jen, so the neater and tidier
Jen works perfectly and
Jenn looks like a typo.