My ex-girlfriend added me on WeChat and said she was getting married, and I said I was going to kidnap her.

If you like her, go get her back, lest you regret it later. If you don't like her, just pretend you don't know. No matter what, other people are getting married, and it is a bit immoral to kidnap her. You'd better settle the matter before she gets married, and don't worry about making things worse at the wedding banquet, which will be bad for everyone. Also, you need to make sure your girlfriend is not joking with you, otherwise it will be a mistake. Hope to adopt it, thank you