You're in good company there, Chelle. And it's one big advantage of wintersowing them- you know what to expect in the milk jug.
Distinguishing between the two might come down to comparing plant habits. The bells are a taller, more upright plant, while the henbit is shorter and spreads like wildfire. If I remember correctly, color is a little different, too. I think the bells are a little brighter green, while the henbit has a more blue shading.
I also have trouble distinguishing the henbit from digitalis and nepeta... I sometimes pull up a bigger henbit which is certain henbit (blooming) and use it for comparison. If all else fails, there's always smell and taste of leaves
Karen