It's the same length but looks a little different because of your hair's natural wave
あなたの髪の癖で少し違うように見えます = It's the same length but looks a little different because of your hair's natural wave
(直訳: 同じ長さですが、髪の癖で長さが違うようにみえます)
髪の癖 = hair's natural wave/curls/kinks
長さ = length