Here are a few corrections:

はじめまして。

わたしは
(Although this particle  は is pronounced as わ, it's written always as  は)

I'm not sure what you meant with the last sentence, but if you wanted to say "I'm not Japanese", the sentence is （わたしは）にほんじんではありません。 If you meant "I can't speak Japanese", then it's （わたしは）にほんごができません。Note that にほんじん and にほんご differ by their endings. にほん means Japan. じん is a suffix for person (so, literally "person from Japan"), and ご for languages.

Good luck with your studies!