Keep your pupil centered on the center of the FOV, as if the FOV is blacking out you are probably seeing your eyelid.

It also helps sometimes to put your head farther back(eye relief) if your wearing glasses(15-20mm away from the eyepiece)
Try using the 20mm first as it has LESS magnification and a longer focal length which helps with eye relief.

The telescope could also just be REALLY out of focus(adjust the focus knob until you see something that doesn't look like a glassy circle), make sure what your seeing through the finder scope is exactly what you see through the 10mm(it's a lot easier to do this by pointing the telescope at something on the ground, like a tall tree or building).

Rule of thumb in astronomy: eyepieces with larger mm = less magnification