I agree with many here that if you love it yourself then go ahead and just use the First. Its one of the best small bags that I've seen across all brands, not just Balenciaga.
However, if you feel uncomfortable anyway, not because of what others think, but because YOU think it doesn't suit you proportionate wise, then I say let it go. But only if its a personal self conscious thing that when you look in the mirror with it, you don't like how it looks. I felt that way about the twiggy and let it go and picked other styles that, to me, looked much better (but again, it was my personal choice not taking in what others said - and I've not regretted it).
I like the idea of carrying a large and small Balenciaga. I have imagined doing it too (should I ever have a situation arise that warranted carrying 2 bags in 2 sizes). I think it looks very chic and coordinated.
Going back to the first though, go with your gut on how it makes YOU feel.
If you could post a pic wearing it though that would help alot. Good luck!