Very good point, Himat.

However, that was not the case for the OP.
I believe he did nothing wrong while flying horizontally at HALF throttle.

He did remain within the engine specifications for that airplane:

Engine: 1.6-1.8 cu in (25-30 cc) 2 stroke
OR 1.8-2.1 cu in (30-36 cc) 4 stroke
OR 1.9-2.6 cu in (32-43 cc) gasoline

If the OP is certain the linkages and instalation was correct, I believe he should bring the incident up to the seller or to Great Planes.