When I load my wife's hybrid into the back of the van, I immediately notice how much larger it is than her mtn bike, or my mtn bike, or my road bike or her previous road bike.
Those things are just huge. I don't know the type of Target bike you have, but I wonder if it isn't just basically huge, also, giving you the imporession, in comparison, of the smallness of the road bike.
Is the path you were riding gravel or paved or what? You didn't say, but if it was gravel it probably is not a good place for a road bike. You likely stated this, and I missed it.
Are your elbows relaxed with a slight bend?
Anyway, give it some time - you are using different muscles.
Good luck!