Plunger in needle

One of the two flat spots on top of the syringe needs to be flush with the white plastic backing. The black plastic halfway down the syringe body is meant to rotate in front of the syringe to keep it from moving around while operating.

What is the sample?  If it's something really viscous the plunger may have trouble going back down.  It may be necessary to dilute the sample in a solvent to reduce its viscosity.

Thank you!  That sounds like it is the problem.

Edit:  Verified this was the solution to the issue.  Thank you again!!

The sample is usually a solvent as I use it to teach organic chemistry in a community college.  We keep it basic to illustrate how a GC works.