XR2206 Amplification problem
A triangle wave TYPICALLY means that you are running into the slew rate limitation of your amplifier.  What's the frequency of the sine wave and what's the part number of the amplifier?  

If that is the case, the solution is an amplifier with higher slew rate.  The max dv/dt  of a sine wave F=A*sin(wt) is found by differentiating F: A*w*cos(wt) and finding the maximum, which is obviously A*w.  So the slew rate of your amplifier should comfortably exceed that value.