I replaced a non-working gas dryer with a new one. A flex line was already connected to the supply line so I used the female end that was connected to the old dryer and tried to connect it to the new dryer. Since the male part of dryer was smaller than the female part of the flex line, I had to use a femal and a male coupler. I used the yellow gas sealant paste on all male threads. I tightened the flex line to the male coupler that I could not turn the female nut of flex line ( using two reaches). Did I over tighten the connections? In these kind of situations is there a danger of breaking or bursting connections, leading to major leak of gas? Thank you in advance

That's a bad fit if you had to use all that sealant, and a fire waiting to happen, sooner rather than later. Turn off the gas and remove the fittings and take them to a hardware store and get the proper fittings. Really, flare fittings used on flex gas lines are supposed to need no pipe dope, but I like to use a little on gas lines. The pressure is usually so low as to not allow a leak to a well-fitting connection. Don't burn the house down; change it right away.