How do I train my dog not to bite me?

I have a 7 week old Labrador and Hound mixed girl and when she first came i started playing tug of war with her and making her chase my hand and i didnt think it was bad and now i realised that it's made her aggressive and now when i'm in bed because she sleeps with me she bites me all the time and she bites hard i spank her on the butt softly and say no but it doesn't work sometime i just put her on the floor and she ends up whining constantly how can i train her not to bite me anymore and regain my authority back before it's too late?