Is it okay if I try? I'm not Japanese either, though, but anyways.

>それなら貸して上げるわよ、と言う。

"About that thing, I'll let you borrow it", she said.

>ていうか重い。

...or should I rather say, heavy.

>うん、でも社交辞礼かなって思って。

Yeah, but isn't that "Shakoujirei", I've just thought...
("社交辞令"="Shakoujirei"="a polite or diplomatic way of putting things" -EDICT. Another typo in the script?)

>というか、オレ以外に殴られたり、呼び出されたのを見たことが無い。

Though I've never seen (him/her/it) being summoned nor attacked by someone other than me.

>「先生には私から言っておくから公欠に…」

I'll tell the teacher, so 公欠に... (I've no idea what's "公欠"...)