I managed to produce (又はmake, draw) something quite cute (pretty)
I was just drawing freestyle but I managed to produce something quite pretty
「結構可愛いのが出来た」= I managed to produce (又はmake, draw) something quite cute (pretty)
「適当に描いてたら結構可愛いのが出来た」= I was just drawing freestyle but I managed to produce something quite pretty
この文脈の「適当に」は英語で「freestyle」や「freehand」になると思います。
「managed to 動詞」は「何とか~する」というニュアンスを与えるパターンです。