The colony (or mine) will try book a freighter to bring it what it needs. It has to know of a place that has the resource available, though. As long as you have mines producing what is needed, it will get there. Eventually.
As far as I know, there are only 3 things that can create "reserverd".
1: Construction. When the base starts to build something, it reserves the materials needed. This is the only time something not there will be reserved. Reserve is higher than amount.
2: Freighters. When a freighter gets a order for something, it will reserve that amount from the available amount at the target mine/port. This will never give higher reserved than the amount, though.
3: Ships/fleet on refuel order will reserve fuel enough to fill their tanks from 0 to full. Once they are done the reserve (for fuel not needed) is released.
4: (in a list of 3). I am not quite sure how colonies treat luxuries...
I have no clue about negative reserved. It sounds like something gone wrong...
If you have a construction bottleneck, there will always be a case of items reserved for construction that are not there. And the construction site will have higher reserved than amount for that.
800 steel and 54000 reserved is a serious shortage. Have you ordered a huge pile of ships to be built there? I don't follow reserved amount much, and there is a phase in early game where you drop your first new colonies and the private sector orders a huge pile of ships.
This is a good moment to visit the expansion planner. On the table on top, sort by your demand. The steel should be high. This is a sum of the "reserves short" as far as I know. Compare this to your amount. If you have a small demand and a large amount you got enough of the item, but not necessarily in the right place. This could be a rather insignificant problem if the difference is huge. That table should also say how many tables you got.
In the table down low, you can choose to display "your empire's resource location", and filter on the resource of interest (steel). Click on each mine, and the small map should give a hint on where the resource is.
Show "resources by your empires priority" or something, and you can again filter on steel. This shows known location where you can build steel mines. You can also filter on the "construct" symbol to see if a constructor is already aiming for a steel source for another mine.
In general, the AI is quite adept at getting the needed resources. It can be that for some resources you know no sources, or the sources are in territories of other empires. That should not be a problem for steel, though. (carbon fiber, polymer - they like continentals and can be an issue for those starting on volcanic and such).