Fixing patch up that has gotten 1st coat of paint
You need to sand and then re-coat it will be a bit tougher to sand with the paint on there but it will come off. 
To do a really good job sand just until you see the paper, wipe down with a wet cloth to remove the dust, then apply another coat of mud, I suggest a 12” wide knife or wider for best results you don’t want a thick coat. When put on two thick it shows more shrinkage so a quick sand and fill again may be needed, I shine a light on the work prior to painting , put the light close to the wall and look to see shadows on the other side of the patch. Lightly sand and recoat a wider patch will be less noticeable when you have a bump to hide, when I was a kid and learning it would take me 3,4,5 coats to get it good enough for my dad, today I usually get it in 2, sometimes 3 coats don’t rush it use light coats, And a light to show imperfections, they will be there the trick to hiding them is wider and uniform patch then a light spray texture can make it really look like a pro job.