Probably, even if there wasn't a withdrawal. A UTMA account usually has income and/or capital gains and the account financial institution issues IRS 1099 forms for that income or gains. You Dad has probably been receiving those forms.

If you had enough income to be REQUIRED to file a 1040EZ, then yes you must amend. If you only filed a 1040EZ to get your withholding back, then it depends on more detail, mainly how much income was on your W-2 and 1099 forms