Check out this article from Realtor.com to see what it says if your appraisal comes in low.

http://www.realtor.com/advice/buy/4-ways-to-deal-if-your-appraisal-comes-in-low/?cid=soc_20160303_58890126&adbid=10154047271912871&adbpl=fb&adbpr=35368227870