urgent question about i94 --xiaobaitu,can you answer?

i did not turn in my i94 and my mom's i-94 at border of u.s.and canada when we drove to canada. We are not going back to the u.s.for at least 1 or 2 years. any way i can mail them to INS? will faliure to turn in i94 create any trouble in the future entering u.s. again? my mom's passport has been stamped with entry date to canada, it should be a strong evidence that my mom left the u.s. before i-94 expires,right? but what about me? i am a canadain p.r., no record or whatsoever on my passport at all. thanks a million!