Is the reversibility of light valid when light enters a flat surface and leaves at a curved surface?

Say for example, a light enters a glass at its flat surface at say angle A with respect to the normal, and it leaves the glass at its curved surface at say angle B with respect to the normal, when light then enters the glass at its curved surface first at an angle B will it leave the glass at its flat surface at an angle A again with respect to the normal? Actually we did a class experiment for this the angle of incidence when the light ray entered the flat surface of the glass is 30 degrees with respect to the normal and the angle of refraction with respect to the normal is 20 degrees. But when we tested that the light ray hits the curved surface first at 20 degrees with respect to the normal it leaves the flat surface and is refracted at an angle 17 degrees with respect to the normal. Well, clearly, 30 degrees is not equal to 17 degrees, it is far far not equal. Did we do the experiment right? I'm concluding that the principle of reversibility of light is not valid when light ray entered flat to curve then curve to flat. HELP ME I'M CONFUSED :(