#1. check tire pressure, Front inflated to the maximum. (so the wind don't push you around and road surfaces doesn't make the sidewall flex)(this one advantage to a rear tire mounted backward rotation on the front of your trike)
#2.The rear tires are part of your suspension, 22-26 lbs. press.
#3.Next air press in rear suspension if so equipped?
#4.Take it to a large LEVEL parking lot and see if it pulls one way or another, if it does have it looked at to make sure the front forks are equal to one another in the triple tree clamps, Or if the rear axle is out of alignment.
If it doesn't pull your the problem.
When riding, understand the steering is a push- pull exercise and locking the elbow on the arm your pushing with makes the steering easier, more confident and results in less fatigue. (especially important for folks without a great deal of upper body strength)
Your using muscles you don't normally use on a two wheeler.
When turning, If necessary learn to SHIFT your bum on the seat so as to be able to plant one foot more securely on the foot peg and better handle centrifugal force.
When going into a turn in the road always make sure your trike is in a gear where the engine is pulling rather than coasting so you can accelerate or decelerate as needed instead of just relying on the brake etc.
Also running your trike in a gear where the engine is always pulling instead of lugging will cut down on front end head shake and give faster response when needed.
by running in a pulling gear if you do get head shake a little acceleration should bring it out of it as well as deceleration or brake application as the riding situation demands. (this is good to know in town on crappy streets)
Hope that helps?