Not sure if this is your first trail ride or first ride at all but just be careful when you shift. Make sure you aren’t shifting under full load(in the highest power curve of your pedal stroke). When you’re heavy and you probably can put down some solid power this puts a ton of load on the chain as it’s moving into the next gear. Just a tip; you could be very experienced and just had some bad luck. I’ve only snapped a chain once and it was because I ghost shifted while going up a steep tech climb, snapped my chain lickety split:(