HELP!

My son is 11 months today and has really bad allergies. I called the nurses hotline on what may help. She said to give him 2tsp of Benadryl. I questioned it based on his age since that’s the entire syringe but she confirmed that was the correct dosage. My son was screaming and super uncomfortable so I did it before researching. Now I’m researching and that is said to be a huge no! What do I do? Is he going to be ok? I’m freaking out!!