I had a heavy piece of metal hit my foot 3 weeks ago. The top of my foot is tight, with a large bump and hurts. I'm wondering if I have a broken bone if it's worth to go to a med clinic for care as I don't have heath insurance?

Yes, but..... A painful bump from trauma is usually a good reason to get checked by your doctor or urgent care. However, a presumed fracture that is 3 weeks old has likely "partially" healed. Nonetheless, best to have it checked as a non-union of a fracture could be occurring. Btw-whether one has insurance or not does not play a role in what is best for health.
Get Treated. I suggest you make an appointment at a clinic that has xray available. You can get treated at a reasonable cost.
Infection. Most adults forget the recommendation to obtain tetanus innoculation every 10 years. Currently they offer DPT (diptheria, pertussis and tetanus, i would recommend everyone get this in case someone gets cut with metal. This being said a fracture or contusions (which also causes swelling) can be seen on radiographs. A minute clinic may be a good first choice.