giving jello to 6 month old totally safe?

Soooo we were eating dinner and my sister in law and mother in law gave my son jelly to " try it out" you know it was fine by me for my baby to try it until they started giving him more and that just bothered me. I went up to my sister in law and took my son away from her and told her to stop giving him jelly cuz that's not good for him and then she had the nerve to say " says who" like are you fucking serious. Normally I'm cool and pretty laid back but my in laws treat my son like if it's their kid  without taking any precautions or they don't even ask me for permission on the stuff they do with my son. And then my partner was right next to me and he said I should relax. I'm so upset that my partner wasn't there to support me. 
Am I overthinking it or was it ok for me to get all mama bear?