Hey!
I'm sorry to hear that you feel this way after the AC - it is completely normal, and I think very few people leave an AC feeling genuinely happy with how they performed.
Most people walk out focusing on what they thing went wrong, rather than what they did well. Try to reflect on the other exercises too, and be proud of yourself for getting through the AC in the first place - that alone is an achievement!
If it helps, I felt completely demotivated after my
Reed Smith AC because I ran out of time on one of the written exercises and didn't get to finish my answer, yet I still went on to receive an offer. You've likely done better than you think, and it can be hard to judge your performance accurately when you're coming down from the adrenaline of the day.
I would try to be kind to yourself and let it sit - the post-AC spiral is very real (and I'd be a hypocrite if I didn't acknowledge that!), but it is rarely an accurate reflection of how you came across. Fingers crossed for you!!