The reason or general reason you break in an engine is this. The cylinder is new, and so is the piston that moves inside the cylinder.
When nitro engine is new, the fit on the inside is extremely tight. The cylinder must get hot, and swell a bit, making the piston fit a bit looser, and making it easier to move inside the cylinder.
The reason for break in is to wear the cylinder so the piston fits nice, tight, and custom without binding.
If you run a brand new nitro engine at a high throttle it it may cause some problems.
#1 The piston fits so tight rather than forming to the inside of the cylinder gently, it can actually scrape off part of the cylinder wall, this can cause grooves in the cylinder resulting in a loss of compression, and therefor power.
#2 Becuase the piston is such a tight fit, it can cause a lot of friction at high throttle, this can cause some overheating. Which can cause internal parts to warp, and distort.
#3 Running the engine at full throttle when your piston fits so tight, causes a lot of stress on internal parts. This can wear rod bearings, and bend or break connecting rods. In short, with such a tight fit, and the piston not seated, you can blow a motor in the first few tanks.
That's why they run them rich for break in, more fuel means more oil too. It provides more lube and cooling when the motor needs it most, at break in.
An answer to your question.
Check your compression. Flip over your rig spin the flywheel with your fingers(with the glowplug in tight). It should be pretty hard to do. If it spins over almost freely you've lost some compression, and power.
If your engine still starts and runs, and you still have compression. No you most likely didn't hurt your engine.
Make sure you continue your break in as per the instructions in the manual. Make sure to let it cool inside if it's cold in your area. Nitro engines need to cool slowly to avoid warping, or distorting parts. Don't let it cool outside in 20 degree weather.
