Dynamic ads are currently in open beta testing.
You can view reports about your ad campaign after it has become active. Click on View statistics on the campaign page. This data will help assess the ads generated and user queries for which they were shown.
In the Search queries report, for example, you can see the queries for which your ads were served. You can add search queries that are not applicable to your offer to your negative keywords right from the report.
Read more information about campaign statistics.