I am so tired, stress mode is on

As u know, I sell some of my stuffs and there's a girl who urgently needed to get moisturizer that I had. She asked for discount, then I gave her RM 5 cheaper. Then we had our deal. I sent it to her and she received 2 days ago.
But she complained, as the size is only 7ml. While that time she asked me, I said 15 ml. I said so because that's what I seen from the note at the bottom of the jar.
She said no, it's 7 ml. I said sorry, it was my mistaken.
She said that this problem can't be solved with a sorry.
I was like..? To be honest, for me it's a simple problem and if someone did it to me I will just forgive her. I didn't try to cheat at all. But she made the problem become so complicated.
She asked for refund and will send it back to me.
I said can't refund as once good sold, no refund or cancellation.
And other thing is, as I know she really need it. That's why I sent it immediately after she did the payment. How can u ask for refund if u really need it ?
Maybe she ady got the original size from her sister. She asked her sister to buy for her in Hong Kong.
So finally she said to search what the price for 7ml in market was. I said why don't just give u discount for next purchase. She rejected.
I felt so pissed off. Ya, it was my mistaken. I said sorry and tried to solve this problem in my way. But she kept asking for refund. OMG. Damn fucking annoying bitch. What's wrong with u ?
I wish I won't face this kind of people again. People can be so stingy and calculative even only for RM 5. So finally I did the refund n I hope she won't find me again. I was so stress for lots of problem and busy as I need to pack all my stuffs. But then I had to face a silly problem like this.
It was a bad luck.
Sigh...I want to go back to Indonesia to refresh my mind asap.
I was(am) so stress and did lots of stupid things that were not good. Sometime u just feel like want to hurt urself. And last nite I told my bf. He said that I was stupid, but in the same time he was sad. I hurt someone that love me so much, it's more pain compare to all stupid things that I did. I just didn't know how to appreciate my life >.<
I should say sorry to myself and people who care a lot about me.
Sigh...don't u think sometime when u are emo or stress, u can be so pathetic or dramatic ? Well at least for me =p