your finding coins and your finding metal, doesn't sound like your doing anything wrong. I don't know how much time you have swinging a machine, but it's not a home run right out of the gate, at least it wasn't for me. I had to really work to get to know my machine, know what it was telling me and what it wasn't. If I could make a suggestion, make sure you are digging every sound you hear. You will find that as you hear a tone and dig what you hear, you will start to see a pattern of tones to coins. Displays are nice, but they can be tricky, rely on the tones.
Keep hunting and digging, the more you get to know your machine, the more you will find and be able to disc. out the stuff you don't want, that's just my 2cents
HH
Pulltab Parson