Yes—if your homemade card is close to neutral, you can probably keep using it for casual RAW shooting. A fixed correction may help a little, but it won’t always be perfectly constant under every light source; different materials can shift slightly depending on the spectrum of the light.

The good news is that your test suggests the card is already pretty close. If the main difference is brightness rather than a color cast, that matters less for white balance than neutrality does.

A practical check is to photograph both cards together, set white balance from the proper gray card, and then inspect the homemade card’s RGB values. If they are close to equal (neutral) and only differ mostly in brightness, the homemade card is good enough for general use.

Since you shoot RAW, small errors are easy to fine-tune afterward. For non-critical photography, even objects that are only approximately neutral often work acceptably for white balance. So unless you need accurate color reproduction, there’s no strong reason to throw the homemade card away.