I will never paint as badly as I do now. I will never paint as badly as I do now.

you need an adverb here (paint badly)

BThis is because I'm making progress, and my arts only gets better with experience. This is because I'm making progress, and my art only gets better with experience.

Only rarely can you start a sentence with because, ie: Because he had learned to swim, he did not drown. (You can also use "since" here) "Arts" cannot take a possessive, but "art" can. Instead of "experience", which you could use but is less common in this context, you might say "practice"