Newby2, good evening.
Suggest you do NOT remove the remaining "bit" of plasterboard that has been shoved back, as the result of the inadvertent "Impact" the remaining bit of plasterboard shoved back will assist in keeping the the filler you choose from simply falling into the void between the Plasterboard and the wall [or whatever] behind the plasterboard.
The filler you propose should be OK.
I think that several, yes several applications of the filler will sort things out.
Fill smooth of with a thin spatula [or similar]
Sand of when the filler has gone hard [suggest next day from filling] BUT use a very, very fine grade of sandpaper + a "Sanding Block" that is a small generally rectangular bit of wood [anything that shape that you can hold will suffice]
Sanding should be firm but gentle, the use of the timber block will ensure that the repair is kept as "flat" as possible.
If you deem it a requirement a third session as above may be needed, slow and steady does it.
Finally, unfortunately the wall will need to be repainted [sorry about that]
Use a Matt emulsion, why? because on a wall, any sort of gloss, eggshell or similar will allow even the best repair shows up like a mountain on a plain.
Ken
