Puppy Class Aggression

Question
I am a little nervous about my 10 week old male golden retriever. He is very loving of new people but a little shy and timid in new situations. I took him to vet this morning and he got his second set of shots and his second deworming. He did great at the vets office. When I took him to puppy class later that night we had two unfortunate events.
I walked into the class and set him down. A very friendly but very small dog came over to meet my dog and I. My dog was nervous and crawled under my chair. He then growled and nipped at the other dog. The trainer took both dogs and had them take turns sniffing each others butts. My puppy is a very large dog for his class (almost all of the other dogs are toy breads with the exception of one hyper lab). He dwarfs some of his fellow classmates.
Everything went well until the end of class when the puppies were given free time. My dog was rolling on his back playing with the lab and two of the other toy breed dogs jumped in on the fun. My puppy started growling and flipped out. The trainer had to push the other dogs away and hold my puppy down on his side. I am really worried. Is this normal golden retriever behavior? Should I be worried about him turning into an aggressive dog? Thanks for any help you can give.

Answer
I suggest you read the following article.  It is a bit long, but it addresses exactly what has happened to you.  If you have any questions after you've finished, feel free to contact me again.

As a note, I hope after reading the article, you will gain a better insight into your dog's behavior, the behavior of the other dogs you may encounter, and may see that the trainer, in my opinion, did not respond to the situation appropriately.

http://www.nesr.info/images-english-shepherd/He-just-wants-to-say-hi.pdf