However, it's important to note that "shy" doesn't usually take a past tense. It's an adjective, describing a personality trait.
We might say:
* "He was shy around strangers." (present tense)
* "She used to be shy, but now she's outgoing." (present tense with "used to")
"Shrank" is the past tense of the verb "shrink," which means to become smaller.