Don't feel low. I went through the same thing! I got ACC at A Level but now I'm doing a PhD.
Yeah the RE would be worth resitting, considering it is AS, but this would increase your workload in the A2 year. You could start again from scratch your AS levels, those grades would make it hard to get into a RG uni (even though RG uni is not the be all and end all in life).
You will learn a lot in life through experience then any exam paper can prove. FYI I deal a lot in the financial markets with my own money, I've learnt to make more money watching how the markets behave than what any textbook can tell me.