Hello, みらいさん
I can advice how to write シ(shi) and ツ(tsu). At first please try to write し(shi) and つ(tsu)in hiragana. Then, according to hiragana, please try to write katakana. I mean シ(shi )in katakana all 3 lines start from same vertical line like し. ツ(tsu)in katakana all 3 lines start from same horizontal line like つ. So please try to write big hiragana and write katakana on it.
And if the first two lines are virtical, it's ン(n). the first two lines are horizontal, it's ソ(so ). がんばってくださいね\(^o^)/