I'm proud of you, even though I don't know much about Coldcard. Completing a transaction using an air-gapped device is very good and the of an SD card to broadcast your transaction on your online PC sounds like a good approach.

I'm not exactly sure how the Coldcard works, but I assume it's similar to using an Electrum wallet offline. However, I could be mistaken tho.

Regardless, what you did is great but I encourage you to continue learning more about enhancing your security.