I've checked on the block explorer and the transaction says completed. And i've heard of that but doesn't it requires 400GB of space to download the full blockchain Cause I dont have that much space on my pc.
What explorer did you use that says it's completed? You might be talking about transaction history in Moonpay?
You must check them on the right explorer like blockchain.com or blockchair.com and the status should be confirmed as the right term not "completed" and to make sure that you already receive the BTC.
About the space problem Armory wallet won't work properly if your Bitcoin core is not fully sync. So the only solution for this is to export private the guide already posted above then use the sweep on Electrum for safety than importing private key in online device.