Inventory/Rack Management
Very interesting project. What to do depends largely on your exact requirements. I guess you have chosen RFID for its easy usage, when everything is set up (like just placing the item roughly at the right spot, instead of needing extra electrical plugs or similar).

I'm not being able to scale it

In a case like this you normally wouldn't use just one Arduino. I would use multiple Arduino Nanos (or similar), each interfacing only a few RFID readers. Then I would use a long range interface (like RS485) to let a master Arduino communicate with all other Arduinos. That way you can faciliate the RFID interfacing code to many Arduinos (which also gives you an easier method of scaling up). Arduino Nano clones are rather cheap (like about 2$ or less I think).

Now items per rack are about 30 that would be so daunting task to place 30 scanners on each rack

Placing 30 RFID moduls per rack is a big task, yes. But that is the price for such a system. If that is too much for you (either in work time or in money), you would need to think about different approaches than RFID. Each approach, that I can think of, will also give you some caveats.

You could use bar codes and bar code scanners on each place. That has a similar difficulty to the RFID approach.
You could give every item an electrical plug, that connects to a fitting socket  on the rack. The ID of the item could then be hold on the item plug by either a number of electrical connections (giving you a binary code) (many electrical lines needed) or by a single chip like an EEPROM (which was programmed with the item ID) (less lines needed).
You could give each item a unique strip with a color code and use multiple color sensors on each place in the rack to identify the item (it has to be put in at the exact correct orientation for reading the colors) (potentially many electrical lines due to multiple color sensors).

All these options are not really better than the RFID option. I would consider the plug with the EEPROM chip the best option from the RFID alternatives above, since these chips can be rather cheap. Though it will be a toll onto the work, that has be done for each item (assembling the plug with the EEPROM chip). Also the infrastructure with the extra Arduinos for every group of a few places in the rack is also needed here.
All in all the RFID option is rather good in comparison to the others. Its main caveat will be the cost, since the RFID reading pads are not very cheap.
Aside from those options, you could make bigger compromises. Big warehouses often have a system, where a worker caries a bar code reader and has to read the bar code of the item and of the rack space, where he will put it. The system can then know, where the item is and if that location is the correct one, and show that on a handheld. That will be way easier to implement, but takes a greater toll on your usability.

I've tried 4-5 RFID scanners with one Arduino uno watching a youtube tutorial and failed.

If you want help with that, you would need to describe, how exactly you failed. Please provide your code, a link to the youtube tutorial and links to any other resources, that you used. Include a detailed description about, what you expected and what actually happened. And put all this information into your question by editing it (not in the comments).
Also as a side note: I've had rather bad experiences with youtube tutorials. You might wanna search for a text based tutorial.