This are jQuery selectors, not ServiceNow, there are a lot of resources when you google.

A solution is to add the :first selector

$j("label[for='"+myId+"']:first").text()

Looking at your code, alternative you could exclude the ones that have the hiddenRadioLabel class in the following way|:

$j("label[for='"+myId+"']:not(.hiddenRadioLabel)").text()

Can you mark the first answer as correct, thanks!