unable to locate package software-centre on chromebook

So i've just installed ubuntu via crouton on my hp chromebook 14, but i need to install software centre as i can't do anything without it.

i try to run apt-get install software-centre

but it returns with the error E: unable to locate package software-centre

i posted my problem on ask ubuntu, but they told me to come over here as crouton is not considered official ubuntu.

Does anyone have any ideas why it is doing this? I am new to linux so please be easy on me!