私の日本語はまだ(あまり)うまくありません。
You need to make clear who the person whose Japanese is not good is.
今以て is rather stilted.
あまり could be interpreted as modesty.
As for kanji of うまい, 上手い is far common in that context.
Besides, the keypoint is the structure of the sentence. 私の日本語はまだうまくありません could be acceptable, but sounds like translationese to me. 私はまだ日本語がうまくありません/上手ではありません is more natural.