If you LBS said it is at .75, they should be able to show you with the chain checker tool they use that it is at .75, which is the recommended replacement indication (for modern chains 9 speed and above. Older 7 speed chains can go down to .5. Nothing immediately dangerous but at the point the chain is worn enough that if it gets more worn it will start to damage the teeth on your cassette. But, ask them to show you, if possible.
If it is really at .75, and you only got 800 miles, take the advice in earlier posts to change some things about the way you ride or take of your chain, or replace the chain more frequently than you would have to.