"
Then a doubt comes to lie at the back of my mind
That I'll offer you me and you'll politely decline (no thank you)
So I hasten to mute it, I'll shout and rebuke it away
There's a negative thought that pops in her mind saying that when she will confess to her love one, that person will politely decline. So she'll immediately remove that thought and she rebukes it because she is sure that what is says is wrong.