Adding Leads to RTP Segments

I'm a bit confused on how people are added to segments in the RTP tool - we set up some segments based on "Lead Database" information, however I'm not seeing anyone in the actual segment. For example, I know there are 3K that should be in one segment as I assigned them the value that is the same as the segment criteria. For example, let's say I know that 1,000 leads in our system have the job title of "Marketing Analyst" and I create an RTP segment whose criteria is "Job Title = Marketing Analyst." Shouldn't I see 1,000 leads in the segment after I build it. Am I missing something?

I was hoping to be able to see the number of people in our database that fit into each segment but so far have had no luck identifying this through the RTP tool. I'd mostly like to just make sure it is working and these people will get our content when visiting our site. Any help or experience those that have used this tool could provide would be most welcomed!