I have trouble with arc

[Termometr]

I get ugly arc
http://www.wrzuta.pl/obraz/fL5vH6t9mC/zzzzzzz
What I can turn up "e" and "e'" ?

________________
\version "2.6.3"

#(set-global-staff-size 20)

SopranyXIA = \relative c'' {
       \set Staff.instrument
       \clef G
       \key e \major
       \time 2/4
       r8 b b b | r e, e' dis |   % 19
       cis r fis,4 | b ais! |   % 21
       b8 b b b | r e, ( e' ) dis |   % 23
       cis r fis,4 | b8 b4 r8 |   % 25
}
\score {
\SopranyXIA
}