Short sale went south at last minute. What did I do wrong?

I waited for 2 and half months for this short sale. Fianlly, bank came back and we agreed upon a price after a couple of counter offers. The listing agent sent the contract to my agent at 9pm Friday night. I got it Saturday morning. Since I was at a seminar the entire day. I signed the contract and sent it over on Saturday evening. It was a cash sale. They ask for an updated bank statement. Since it was such a short time. I was short of $20,000 in my bank account. I attached my investment account which has sufficient fund. However, the listing agent came back Sunday afternoon and said that the seller has accepted another offer because she waited too long. My agent tried to contact her, but no response.

What was wrong in this process? What’s your opinion?