You need to add the Shiba Inu token on the BSC network, you push the add token button and put in this contract address:
0x2859e4544c4bb03966803b044a93563bd2d0dd4d
You should see your Shibas on BSC now.
Make sure you have a few dollars worth of BNB on your wallet and you can transfer the Shibas back to Binance (use the BEP20 deposit address from Binance).
Once you have them on Binance, transfer them again, but in ETH20 network to your Metamask wallet and you should have them in the correct network to stake them on Shibaswap.