You are not out of time to amend your 2018 tax return. Your have 3 years from the original due date of the 2018 tax return or until April 15, 2022 to file an amended tax return for tax year 2018.
You should file your 2020 tax return with a Form W7. When you receive your ITIN, you can amend your 2019 and 2018 tax returns to claim any additional credits you may be entitled to.
File Your Return & Request An ITIN
