Why is my oscilloscope reading jittering, and how might I fix it?
There is not a lot of information here, but when I see students with jittery sine waves on their oscilloscope screens it is almost always because they haven't set their trigger level well. If your scope has an "autosetup" try that for now (and learn how to set up an oscilloscope), but in general set the trigger near the zero-level of the scope. At the zero level the rate-of-change of the sine is maximum and the jitter in the display will be minimum.

Edit: Chris Stratton's comment is quite right.