At present there are 3000+ unconfirmed transactions.
Correct.
But why the newly found block adds only 8 of them to the block chain??
Because that is the number of transactions that the block builder included in their block.
who controls how many will be added to the block chain??
The person that builds the block (or more specifically, the software that is being used by that person).
When a solo-miner or mining pool builds the block to be mined, they get to choose which valid transactions (if any) they want to include. As long as they only choose valid transactions, and the sum of weights of all the transactions that they choose doesn't exceed the block weight limit, the block is valid.
I do not know who controls,
Then, instead of making a ridiculous nonsense guess, perhaps it would be better for you to just wait until someone that DOES know answers. Then you can READ and LEARN.
but maybe this happens through downloading the network because of the panic
No. Just No. Please don't spam this forum with absolute nonsense. It is a waste of your time, and it makes the forum much more difficult for everyone to use.