I was stopped for not wearing a seat belt as I was leaving a bar, but I was. It will be his word against mine, what r my chances

There are too many variables to know what your chances are and you should probably discuss them with an attorney rather than post the facts of your case here. However, if you want to fight the charge, you can plead not guilty and go from there. You can choose to have a jury trial or a trial by the court. When there are two competing versions of the events, it's anybody's guess as to whom the jury/judge will find more credible because it depends on so many different things.

No one can tell you ahead of time what will happen. However, a local attorney can probably give you a good idea about what is common for your city, this type of offense, etc.