Technically, yes, but it's not the usual phrasing. But it would sound better to say "If this were up to me, I would gladly help you." or "If it was my decision, I would gladly help you." Hope that helps :)

I agree with Megan. This is correct here in the US too, but would probably be worded differently; for instance, using one of the other phrases she provided.

"If this depended on me, I would gladly help you." Note the comma after the first part and the period at the end of the sentence. 'It' could also be used to replace 'this'. Other than that, it's all good.