Iwas quaking from head to foot l, and could have hung my hat on my eyes, they stuck out so far. a oxymoron

It's not an oxymoron. It is a metaphor.

Explanation:

It compares an object to an action, and it is not literary applicable.  The metaphor "could have hung my hat on my eyes," this means that they were so surprised/frightened that their eyes were very wide. Picuring someone's eyes as wide enough to hang a hat is part of the definition of hat a metaphor is.

comment ur email above in the comments(:

c, have a good day ~matya