Actually, I feel that the ですが。。。ですが。。。 does feel a little repetitive and awkward to me, but that's a pretty minor thing. You could remove the last が as one option to remove the repetition.
However, I think what's most important here is how you express the rest of the sentence. First, saying "下手" sounds overly blatant, especially with the なん after it to make it sound more factual. I would personally start with something like:
僕はちょっと苦手なんですが。。。
僕はあまり上手じゃないんですが。。。
Personally I would use ”〜ですけど”, but there is nothing wrong with "〜ですが”
For the second part, I feel that "手伝えるといい" doesn't sound like a very commonly used phrase. Instead, the expression "役に立つ" (to be of use to) or its more polite form "お役に立つ" jumps to mind.
So you can use this for the second part:
お役に立てれば嬉しいです。
Or, you can actually omit the 嬉しい part and use a common abbreviation for this:
お役に立てればと思います。
僕の回答が少しだけでもお役に立てれば幸いです (^^)