What should I be concern with a fiiling that fell out of my root canel? Okay its my last tooth on my right bottom side. I got a root canel and was suppose to get a crown, however insurance didn't cover it. So the filling fell out and now I feel something

Infection. If the filling fell out the tooth can get infected and to retreat the root canal is difficult and costly. I am not sure how long ago it fell out but you can have it sealed (not re-filled) to prevent bacteria from entering the root canal system and causing an infection and get the crown as soon as you can afford it. Good luck.
Loss of tooth. Get a filling placed immediately. The root canal is now in direct contact with the oral environment and bacteria will re-infect the tooth without treatment. As stated by others a crown is most likely indicated, but at the very least get the tooth sealed with a filling to prevent re-infection. You will still be at risk for the tooth fracturing but at least it you are protecting the canals.
When . When you lose your root canal filling you have a direct path from your mouth straight into your bone which has little defense against the bacteria that will find it's way in there. You do need to see a dentist to at least clean it out and re-seal it. Shame on the insurance that doesn't cover it but don't let that stop you from saving some money and taking care of it yourself.
The . The biggest concern, if there is no problem with the root canal, is that the tooth is at increased risk for fracture. Typically, teeth that require root canals have a history of significant decay. This loss of tooth structure, combined with the fact that the tooth can become brittle after a root canal procedure because both the nerve and blood vessels are removed, leads to a weakened tooth. This is why a crown is the recommended restoration because it is the best way to protect the tooth. The fact that the filling fell out of the tooth indicates that either you have decay, a fracture in the tooth, or the filling broke. All of these issues require the services of a dentist as soon as possible in order to correct the problem and prevent loss of the tooth (which leads to a whole new set of problems).
If . If a tooth that has been treated with root canal therapy does not get crowned, the probability of it fracturing, leading to an extraction, is very high. With the filling having come out, there is a good chance the tooth has started to fracture. With the filling out, the canal system likely will get reinfected, leading to chronic infection and inflammation, and usually pain. You should see a dentist asap.