Hole in wall, need to fill and put in screw plug - what filler?

hello
so the auld fella went hammers and tongs at the sitting room wall last night putting up a curtain rail.

The ends were OK, he got the rawl plugs and screwed in the holders so they're looking OK but then in the middle they're seems to be a lintel (s?) and while trying to drill for the raw plugs, it seemed like we need shorter screws (due to lintel) and now also need something to fill the holes in the plaster.

If anyone has seen the Simpsons episode, where Homer makes the BBQ, this would resemble his demeanor yesterday evening :pac:

so I'm assuming I can fill the hole and then set the rawl plug in there and afterwards get a shorter screw for the job?

Am I right? If so what is best filler for the job?

If I'm wrong, first of all, go easy on me, DIY aint me strong point - secondly, what should we do?

thanks