if you e-filed and did not check someone can claim you as a dependent but someone did file claiming you as a dependent your return will be rejected with a reject code. there's no way to fix this to enable you to e-file. Your return will have to be mailed. Sooner or later both parties will get letters from the iRS to maned by not claiming the dependent. if neither does, the IRS follows up with a second letter requestion proof on entitlement to dependentcy claim.
From your standpoint the law is not whether someone actually claimed you but whether someone is entitled to claim you even if they decide not to.
