If the stain did not take, there are techniques to try and improve the colour.
One is firing the silver stain face down on a sifted and smoothed out bed of whiting or thick ceramic fiber paper.
Another is to re-apply your stain and fire again between 675°C (1250°F) and 760°C (1400° F). The higher heat will help the silver stain "take" to the glass. Fire the silver stain face down because the higher temperature will melt the high fire tracery and matting resulting in kiln-wash sticking to the painting.
A third method is to use hydroflouric acid to remove the stain and so start again with clear glass. Remember this is an extremely dangerous chemical.
After a second successful firing, be sure to discard the loose whiting or shelf paper from your kiln-shelf as any residual silver stain absorbed during the firing can result in yellow spotting on your glass on later firings.