Miscalculated social charges as a micro entrepreneur

I think I have made a few mistakes during my micro-entrepreneur-ship and I wonder what I should do.  I think I may have misunderstood what I have to declare for social charges and (as a result) have not paid the charges required. I’d be grateful for some advice on whether I’m correct. I thought I only had to declare earnings for the work I did that needed to be taxed in France. Having read more widely I think I have made a few mistakes.
I have (so far) submitted two trimesters worth of accounts.

1. In the first I declared nil earnings despite earning from a salaried job in the UK (before being made redundant) because I thought it was exempt as I was paying UK tax and insurance. I also received an income from an early pension (also taxed in the UK so I thought this was exempt).
2. in the second trimester I declared some earnings for work I did in France - but (again) not for an income from my monthly pension (taxed in the UK). By this time my redundancy had kicked in so I no longer had a UK salary (but I did have some redundancy pay - and I’m not sure if I should have paid charges on that - I was told redundancy pay is exempt from tax - but not sure).
3. Am I correct that I should have paid social charges on all this income? (I am not signed up to the tax-as-you-go system - just social charges.) And if I have made a mistake what options do I have - will they even know? Will I get fined?

Any advice would be very welcome.
Thanks