請問賈斯汀這首英文歌是否有唱錯?文法句型?

聽這首歌覺得有些奇怪有很多地方不符合文法？包括I=我應該是在每個地方都要大寫才是為什麼他使用的全是小寫？(我有一些修改過了)像這樣的文法句型有錯嗎？還是唱歌時不拘文法？
Justin Bieber《That should be me》 聽歌：http://www.wretch.cc/album/show.php?i=lov2979486z7&b=1&f=1846430115&p=2 everybodys laughin in my mind
rumors spreadin about this other guy
do you do what you did when you did with me
does he love you the way I can
did you forget all the plans that you made with me
cuz baby I didnt

That should be me, holdin your hand
That should be me, makin you laugh
That should be me, this is so sad
That should be me, that should be me
That should be me feelin' your kiss
That should be me, buyin you gifts
This is so wrong, I cant go on
do you believe
That that should be me
That should be me
yeah

said you needed a little time from my mistakes
it’s funny how you used that time to have me replaced
did you think that I wouldnt see you out at the movies
what cha doin' to me?
your taking him where we used to go
now if your trying to break my heart?
its workin, cuz you know

that should be me, holdin your hand
that should be me, makin you laugh
that should be me, this is so sad
that should be me, that should be me
that should be me feelin' your kiss
that should be me, buyin you gifts
this is so wrong, i cant go on
do you believe
that that should be me

i need to know should i fight for love
or disarm its getting harder to shield
this pain is my heart

that should be me, holdin' your hand
that should be me, makin' you laugh
that should be me, this is so sad
that should be me, that should be me
that should be me feelin' your kiss
that should be me, buyin' you gifts
this is so wrong, i can't go on
do you believe
that that should be me