Your result may be fine. A flat-looking scan does not necessarily mean the negative or development is bad.

For black-and-white film, the negative is only one step in the process. A good negative often looks somewhat flat because it preserves as much information as possible. Final contrast is usually added later, either in darkroom printing or during scanning/post-processing.

What you want in the negative is usable detail in both shadows and highlights: shadow detail should be present, and highlights should not be blocked. The idea is often summarized as “expose for the shadows, develop for the highlights.”

Also, a flatbed scan is not the best way to judge fine grain, sharpness, or even tonal quality. Scanner settings and scanner limitations can make a good negative look weaker than it is. To assess the negative more reliably, examine it directly on a light table with about a 10x loupe. That will give you a better sense of density, sharpness, and grain.

So: don’t judge too much from the raw scan alone. If the negative holds highlight and shadow detail, and you can add contrast successfully in printing or editing, you’re likely on the right track.