If you turned the ignition on and or moved the magnet past the sensor then you did in fact pop the sensor. You have a CH Ignition on your engine. That ground wire can be attached to your engine or mount if it is metal with a ring connector also. However wrapping it around a small hose clamp attached to the hex portion of the spark plug is more secure in my opinion. I have tried both ways and I have converted many 44 and 50cc Echo engines. Same as your BME 50. I also use CH Ignitions in all of my conversions. If you feel the clamp idea is "ghetto" then send the box in to CH and they will convert it to a Bosch cap boot and you will have a different look. As for the sensor, BME had a small aluminum tang they JB Weld the sensor to as do many of us for conversion engines. Call CH and get another sensor with the Dean's connector already installed, with the old sensor still in place scribe a line along the tang and the engine case for an index mark. Now remove the screw holding the sensor to the case, remove the sensor and residual glue from the tang. Mix up some JB Weld and glue the new one on while making sure the sensor faces the correct way. On mine the letters on the sensor face the timing ring. Reinstall it on the engine using your index mark and you are good to go. No you will not be out of time as you have some tight tolerances there. I have done this many times this way for my own engines and for other people. I have double checked the timing after doing this and it is correct too. Just remember to never, that's never power on the ignition if the ground is not connected and properly grounded.