My SE tracks and hovers fine with no right thrust added.

That's were I usually put the washers between the mount and the firewall. Start out with 1 washer and go from there. You will need two washers though 1 for top and 1 for the bottom on the left mount. I usually use #8 washers for this task because they are thicker than the smaller washers.

Also make sure your rudder is trimmed out. With the cheap plastic pushrod tubes my rudder and elavator will change with the temp.