for 2020,
1) how much income is reflected on the W-2? if it is under $12,400 you have no requirement to file a federal tax return. HOWEVER, if there are federal tax withholdings, the only way to get the money back is to file.
you MUST check the box stating you CAN be claimed by others. SInce you did not file yet, there is nothing to amend, you just have to file (if necessary)
2) you may have to file in CA regardless, depends on your income and the state rules for CA. Also need to file in any state you worked in, subject to taht state's filing requirements.
for 2021, this appears to be more of a problem. Even though you filed already, unless there is a good reason, (and avoiding state taxes is not a good reason) you still CAN be claimed by your parents (whether they did or not doesn't change whether they CAN; they have the option not to). The federal return will need to be amended, adding the missing W-2 to the equation and then adjusting the filing status stating you CAN be claimed as a dependent, which would remove the $1400 Recovery Credit that probably appeared on Line 30 of your tax return.
if might be worth you and your parents engaging a local tax specialist to review your and their 2021 tax return. I wonder about whether there are educational tax credits that they are not realizing because they didn't claim you. There are a number of things to adjust on your tax return; it just might be easier for someone to help y'all out locally. The risk is the problems created already may get worse........
