If you already e-filed, look at your Form 1040 and see if the box is checked that says you can be claimed as someone else' dependent. It will be seen in the top half of page 1 of the 1040, near the words Standard Deduction.
If you have not yet e-filed and need to correct your answer to this....go to MY INFO and click your name and then go through the screens to the question that asks if someone else can claim you as a dependent. Or--if you messed up and already filed ---wait for the return to be fully processed and amend. Meanwhile that means the person who can claim you is being rejected and will have to file by mail now.
You would see that on the first page of your tax return Form 1040, underneath the Standard Deduction title where the box would be checked that says Someone can claim you as a dependent:
To view your form 1040 and schedule 1 to 3: