My temporary comes loose when eating, will this happen with the permanent one?

I had my bottom right molar pulled. I have the temporary crown on but I'm have trouble eating anything without it coming loose. The temporary came loose eating a baked potato 7 hours after putting it on. I went back and they fixed it. That evening in was completely off. I used dentteck and put it back myself. I'm scared to eat anything. Is it because I don't have a tooth on the other side? Will this happen with the permanent one? I fear I'm wasting my money. Thanks