It's worth pointing out that if the Universe was finite in diameter when it was "created", then it would be finite in diameter now. But that is not what is believed to be so. Space is likely to be infinite, in which case it was infinite to start with.
I'd be happy to discuss that with you further beso, but what's certainly true is that the Universe wasn't a Planck Length big, and it's also not true that the Planck length is a minimum possible length scale, ie that there are no possible smaller distances. That would have severe consequences for Special Relativity, in fact. What *is* true is that the Planck length is the smallest length we can claim to understand at the moment.