Help please i really need it?

Ok i have a 15 week old labrador german shepherd mix puppy he weighs 25.8 pounds i had some company over and my friends daughter gave him a whole milk chocolate Symphony bar by Hershey's the size of the candy bar was 1.5 oz. (42g) he ate it about 1 hour ago is he going to die or have a seizure or something else serious im really worried would the effects of the chocolate be worse seeing as he is a puppy and not an adult dog or does it just simply go by weight and sensitivity. Please help no rude answers please thank you.