Would she want you to stop buying her things if she's not interested? Well, a decent girl who wasn't interested would be returning favours to you so that she wasn't in your debt or misleading you. But a girl who will take advantage will love having stuff bought for her and have no regard to how you feel.
That being said, I'm wondering why you *told* her that you'd stop buying things for her. Why didn't you simply stop doing it without mentioning it? It must have been a very awkward discussion.
Never regret anything that has happened in your life. It cannot be changed, forgotten or undone. So, take it as a lesson learned and move on.