Getting Indexed vs Sitemap

So if I have a site that has 500 pages.

All 500 pages get indexed in Google (I manually check this through site:mysite.com).

I then add a sitemap to Google Search Console (Webmaster Tools)
and find out that only 130 pages are getting indexed.

Will this discrepancy effect my rankings in Google in the future?

That doesn't make sense. Maybe one of the two is not updated?

I was under the impression they would match up.

Did you check the pages manually on Google SERPS? Eventhough Google shows 50 pages with 10 results per page, sometimes when you reach the 4th page you could hit the max limit.