Unwanted turn can come from a number of sources, including: rudder offset, one wing heavier than the other, warped wings, warped fuselage, stabilizer tilt, etc.
Please describe your glider in detail (ex. Kit or from a particular published plan, or self designed 1/16” sheet rectangular 3” width wing with 15” x 3/32” thick x 1/4” deep tapered to 1/8” at the tail fuselage and ... dimensions for the stabilizer and rudder, and weighs...grams).
Also please describe the turn. Is it hooking on launch? Turning too tight of a circle in glide?
Also please describe your launch device and launch details (ex. Launcher 6” x 3/16” wood dowel with 6” loop of tan sis rubber; launched at 45 degree angle with 10 degrees of bank in a 25 ft. Ceiling site and launched to about 20 ft.).
With this info, I can provide some specific suggestions.
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