It's too short.
'Corto' — 'KOR-to'. Hard 'c', clear double stop before 'o'. Don't make it sound like 'chorto'.
When a skirt, dress or trouser leg is shorter than you'd like. Common feedback after trying something on — very clear and simple.
'Troppo' (too) + adjective. 'Corto' = short (of length). 'Basso' = low (of height). Don't confuse them. 'Corto' refers to item length; 'basso' refers to vertical position.
È un po' troppo corta per i miei gusti.
It's a little too short for my taste.
Adding personal preference qualifier
Non mi arriva al ginocchio.
It doesn't reach my knee.
Describing the specific length issue
Preferisco qualcosa più lungo.
I prefer something longer.
Expressing preference rather than criticising the item
Italian women are generally conservative about hemlines in professional and formal contexts. 'Al ginocchio' (at the knee) is considered universally appropriate. In churches, skirts must cover the knee completely.