Hello, I am a re-beginner (I pick up the guitar after many years) I am working my way through the lessons and now I am at country level 1 5: root 5 strumming B7 and I do not understand the theory.

I got it for E chord, you strum the E and then the fifth scale E1 F2 G3 A4 B5 so B

for the chord B7 it is F# but if I apply the same logic it goes B1 C2 D3 E4 F5 , it is obviously not F as it sound very wrong.

Can someone explain what is wrong in my reasonning?

Thank you in advance.

Joss.