Hey Apple, I saw your character and she's looking good! Tsunderes tend to be among my "preferred archetypes" and so I'll try to offer you some advice.
I tend to make my tsunderes overly emotional, though this is often hidden under a cloak of indifference. Most tsunderes are known for being notoriously hot-headed and their trope typically implies that they have a love interest that they will frequently act angry and sometimes even hateful towards, but more often than not, they will try to show affection to said love interest while trying to retain said air of indifference. It's true that not all tsunderes are hot-headed and some try to act "cool", but they will act flustered regardless towards their love interest.
tl:dr; Tsunderes are known for being indifferent and often in denial, especially in regards to their love interest. If you want to make your character more of a "tsundere", give him or her a hidden talent or genius that they are trying to hide from the world, a hot-headed temperament, a love interest that they can be flustered around, and maybe a secret that they just might be hiding.