My 8 month old German Shepherd just started a group obedience class and 2 of the dogs in class were littermates. They were reactive to my dog and my dog was barking and lunging towards them. The trainer says that I am the problem because I'm anxious. What should I do?

I have an 8-month-old GSD who is very sweet-natured and who I have been successfully working on engagement and luring training since I got him at 8 weeks. He has played successfully with several other dogs that I knew well enough to allow that interaction and had no signs of aggression. However, I started him in obedience and the other two dogs in the class were littermates belonging to a mother and daughter. They were reactive to my dog and began lunging and barking and he lunged and barked in return. I was able to redirect him enough to finish the class even though each time we went to class we had the mutual reactivity going on. We are now in a Star Puppy class at same club and my dog is very leash reactive to all the dogs there. I've continued the class by being behind visual blocks in a corner and working with him there. He does pretty well so long as I keep him redirected but still goes off if he "sees" a dog. Trainer says it's me as I am anxious and I am! Am I making a mistake taking him?