I just sorta had one go wrong myself, though it's really not that big of a deal.
Basically, I gave my mare a shot of Lutalyse five days ago to induce a heat cycle so I could breed her to the 'stud of my dreams', a chestnut TWH named Leroy.
She came into heat yesterday evening, so this morning I visited my neighbor who owns the stallion and told him. He brought his other stallion (a black TWH named Bear) up to tease my mare to see if she was receptive or if she needed another day to fully come into season. She was receptive.
I don't blame my neighbor at all. He's been breeding horses for decades, and he is older and tends to forget things nowadays, and, thinking about it, the chestnut TWH (Leroy) wasn't the best match for my mare in the first place (and I have been debating lately over which stud to breed my mare to, lol)... but he forgot that we were just teasing my mare with Bear and bred her to him.
I'm not fussed, though. The main reason I had chosen Leroy in the first place, besides the fact I've wanted a foal by him for about ten years now, was because with Leroy, I'd have had a higher percentage chance of getting a filly. Bear is honestly a better match for my mare, I think... he's got a shorter back whereas hers is a little longer, he has a more refined and thinner/higher set neck than her, etc...
So, if my mare takes, the resulting foal will be a full sibling to my gelding Dakota.
*Crossing fingers and hoping for a filly*...