Postscript: Color-coding by Purin-chama.
"Senpai" is much like an honorific used to address people who are older than you and generally serve as mentor role figures [thus there is common use in schools].

ああ　うまく出来ません
歌が好きな私って

ああ　なぜかあまのじゃく
素直な子になれません

でもきっときっとあの人も
同じように　スネてて
電話の前で「もじもじ」かも～

今日の私　美人ですか
自信持って　電話していいですか
今日の私　色っぽいすか
まっすぐに　打ち明けて平気ですか　先輩

LALALA...
先輩

"senpai!"

aa  umaku dekimasen
uta ga suki na watashi tte

aa  naze ka amanojaku
sunao na ko ni naremasen

demo kitto kitto ano hito mo
onaji you ni  SUNEtete
denwa no mae de "mojimoji"
kamo~

kyou no watashi bijin desu ka
jishin motte  denwa shite ii desu ka
kyou no watashi  iroppoisuka
massugu ni  uchiakete heiki desu ka  senpai

LALALA...
senpai

"ganbarimasu! senpai"

"Senior!"

Ah, I can't do it well
Even though I love to sing

Ah, it's perverse for some reason
I just can't seem to be true to myself

But surely, surely, that person too
Might be sulking like I am
Maybe "fidgeting" in front of the phone

Am I a beauty today?
Is it okay if I call you with confidence?
Am I sexy today?
Is it okay if I look at you in the eye
and open up my heart? Senior?

Lalala...
Senior

"I'll do my best, senior!"