I AM A PERMANENT RESIDENT ?

At this point i can’t help to be nervous and scared i came to florida when i was 4 years old and got my residency card on 2010 with my mom i have been reading that even the permanent resident can also be detained by ICE ? Can someone please help me understand if i should be scared of getting deported? If they stop me can’t i just say yes i am american or how do they even check ? I learned everything here what exactly am i going to do in cuba…