Sent Bitcoin Cash to Coinbase vallet I wanted to convert the Bitcoin to Bitcoin Cash. Using changelly I did that succefully but sent it back to the same Bitcoin Wallet. So, that mean did I lose my money? I am completely new to this. Is there anything I can do?
bitcoin sent from coinbase will come from a wallet they control. if you sent bitcoin or bitcoin cash back to it they now control those funds.

the proper course of action is to document the process, what addresses was used, which transaction ids was assigned and what blocks did the transactions get mined in, then contact coinbase customer support and request that they help forward those funds to an address you control.

do it as soon as you can, but be aware that you might have to wait until coinbase supports BCH to withdraw them.