问使用ggplot2绘制地图，在填充颜色时遇到问题？

最近在用ggplot画地图，在填充颜色时遇到了些问题，我如果直接用我的代码绘制，geom_sf(data = land, aes(fill = Class_Id))，得到的地图是渐变填充。可是我想具体区块具体填充，于是在这句后面添加代码为scale_fill_manual(values = c ("11" = "skyblue","12" = "orange3","21" = "seagreen",

"22" = "seagreen3","23" = "seagreen1","24" = "seagreen2",

"31" = "olivedrab3","32" = "olivedrab2","33" = "olivedrab1",

"41" = "royalblue1","42" = "powderblue","43" = "purple4",

"46" = "seashell1","51" = "sienna1","52" = "snow","53" = "grey82"))

可是最后得到警告Error: Continuous value supplied to discrete scale，

在此向各位大神请教