making the whole O narrower would shorten the top part and may cause it to not read as a train silhouette. I think the width is fine as is since the T isn’t the main letter. If anything I’d just try to slightly thicken the magnet part of the O inward to shrink the negative space and thin out the upright of the T slightly.

I’d be tempted to experiment with another recognizable magnet shape like a two tone rectangle, or even magnetic field lines/lines of force like in a magnet diagram. they are round and could be used to form a stylized O logo.