Buyer's agent asked for 3.5 percent on a 2.8M listing and I said yes without thinking

Signed the listing agreement at 2.5 to the sell side and had a verbal with my agent at one. Buyer's agent called two days later representing a client who had already seen the property off-market and wanted to write. She asked for 3.5 and I said fine, I'll cover it, because I wanted the deal and did not want her to walk the client. Offer came in at 2.61M, we settled at 2.675M. My carry was 21k a month and I was at month nine. The 3.5 cost me 93,625. The one point I had already promised my agent cost me another 26,750. Total commission side was 120k on a deal where my projected margin was 190k going in and actual was closer to 140k before that conversation. I made money, just not the money I modeled. The lesson for me is not about commission rates, it is that I agreed to a number while I was relieved the buyer existed, and relief is a bad negotiating position.