I'm no expert, but this quote says most of it. However, you may end up fine...sometimes you just never know. If they yeast aren't stressin' all that much then you won't have to worry about it. But, they may hit a point where they just can't eat any more and that's when the higher gravity beers "stick" at too high a gravity for what you wanted. If you have another pack layin' around, I'd chuck it in there - I had to do that once before because I only pitched a single packet into an RIS that was at 1.084 or something. My LBHS guy told me to add another packet...so I did. Healthy pitch rates can really help your beer turn out better. Good luck either way!
https://www.homebrewtalk.com/showpost.php?p=883439&postcount=10
https://www.homebrewtalk.com/showpost.php?p=883439&postcount=10