Hi!
First of all get ride of all the sloop in the system (aileron,rudder and elevator)! Second use 100% throw or more when it comes to throw on all channels! You fix the throw mechanicly first and then just do some minor electronic trim.
On a trainer no expo is needed! Just trim it out right and fly! Never ever couple the side rudder to the ailerons!!!
If you can't trim it out yourself ! Get help from a friend in your club who can! -You are a member of a AMA club aren't you!