The B7 open chord is a little bit of a crazy one. It can be quite a difficult chord to learn, mainly because it demands the use of all four fingers and the layout is a bit tricky.
One of the ways to memorise chords like this, is to try to see some kind of geometric shape. For example, here, fingers 2, 1 and 3 create a triangle. So I divide this chord into two sections; Firstly the triangle, created using fingers 2, 1 and 3 and Secondly, adding the little 4th finger on the 2nd fret, first string. I don’t look at this chord as a whole 4 note shape, I see it firstly as a triangle, with an additional note on the 2nd fret, 1st string.