Those fixings are fine for lightweight stuff but not what you want here: you should use something like a "toggle fixing" if you have space behind the plasterboard (which should be the case in most interior stud walls.
https://www.screwfix.com/c/screws-nails-fixings/spring-toggle/cat840118
I also agree with the other comments that you should try to fix into the studs where you can: a stud finder is ideal, but you can find the studs by simply knocking on the wall. Areas between studs (where you should use toggle fixings) will sound hollow and loud, and "give" slightly when you knock firmly - a bit like knocking on the side of a box. The places with studs will be much more muted and quiet, and will feel harder with no give - more like knocking on a piece of wood.
Mark the studs with a pencil or object on the floor, and then when you think you've found a few of them, check the distance between them - they should be almost exactly either 40cm or 60cm apart if the wall was put up properly, with the first one around 40/60cm from one wall (usually the exterior wall for the house). If they line up with one of those distances then you can be fairly confident you've found the studs, and your best bet is to simply attach to those with wood screws
