The Crazy Day of a Customer Representative

So today was hectic, and I blame myself for it.
A male customer wanted to redeem a survey coupon.  He had told me when he was ordering that he wanted three McChickens and wanted to redeem the coupon.
After reading back his order the first time, I can't remember what he said, but it was something along the lines about the order not being right because of the price.
Thus, I fixed the order and after some questioning (which might have been where I made my error) I asked him if the order was supposed to have been for four McChickens altogether.  Low and behold, that was what he wanted.

After exchanging money and giving him his change, he asked me if I always had this attitude. 

It was then I realized that I must have made some mistake, for he then proceeded to tell me a few things...
#1. This wasn't the first time that the attitude in question had been displayed from me
#2. He wasn't the only customer, which I understood because there were a few customers in the past that said something about the said attitude
#3. If wasn't going to have a good attitude, I should have been in the back

I told myself to not get upset or allow my emotions to get involved because if I had allowed myself to get terrified and cry, it would only make the situation worse.
I can't say that it helped the situation because he demanded a manager, my name, the store number, and even the corporate number.

Where were my emotions in all this? 
They weren't there: now that I think about it, I feel like a sociopath... or at least I did until I had some time to myself.
Now I just feel physically ill.

One of the people that I work with didn't really help matters: she asked me if I was worried the manager was going to do anything.  For some reason, that question felt like a horse's hoof hitting me in the chest.
After thinking it over, I told her that my trust wasn't in the manager - it was in God.
It was God who got me this job, and it will be God alone who decides if/when this job ends.
If this was how God wanted me to close this chapter of my life, then so be it, okay?

I suppose this means that I do have feelings about the situation.
I feel bad for what I did, but I can't take it back...
I admit I did wrong and just have to try better next time...
Even if that next time is decided by God to not be there.