Not sure what advice to give, other than you'll be far less frustrated (and probably develop fewer bad habits with tension and picking) if you wait for your proper picks to arrive, and find a new padlock to work with.
The combination of hairpins and a rusty, grimy old lock isn't going to be giving you very clear feedback on what you're doing with the picks... so I think it's pretty understandable (and normal) that it would be causing you some frustration.
