First of all, congrats, you are on the right place to avoid getting scammed.
I have recently bought $100 bitcoins (the guy that helped me said this was the minimum) and added them to my Blockchain Wallet.
This is a lie, you can but $0.1 if you want, there is not minimum.
Now, 48 hrs later, I was paid something like $920 into my Blockchain wallet but it says it is Non-Spendable.
This is weird, maybe you have to wait a couple of confirmations, but should be spendable
Now, this guy that helped me says I must add ANOTHER $300 to the wallet before that $920 becomes Spendable.
This mother fucker is trying to scam you. There are 2 options, or he have access to your blockchain wallet, or he have a backup from your private key.
So... what to do now.
Open a new wallet, and move your founds there. Never give access to no one to that wallet and hold your bitcoins in your hands. If you need some support to do this i could help you, just send me a personal message.
By the way, move fast before he takes your money, but let him think you will depo more