hi, and welcome to the forum.
okay, this is not that unusual, but i want to take a quick moment to let you understand that how you phrase any help requests is very important.
in this case, it's a simple miscommunication, i think - you say you built the mission yourself - now, you obviously mean that you created a mission inside QMB in this case.
when we talk about 'creating' missions in this community, we usually mean actually creating it inside FMB (Full Mission Builder) - in other words, from scratch, adding all other objects, vehicles, ships, etc.
when you make a mission in QMB, it's not necessarily a 'clean' mission. in other words, it's a QMB mission that was pre-built, either a stock or user made one, where objects such as targets, etc are already built into the map.
only some open slots for planes are kept, so that you may use it as a QMB mission.
there are guidelines to building QMB missions, you'll just need to read them to find out more about this.
back to your issue, though - the reason you are seeing these extra, unwanted flights of planes is that they were also built into the mission, as non-selectable planes, so you will see them every time (in that specific mission)
i'm personally not a big fan of this practise, preferring to fly QMB missions without any other planes than those i select.
there's not much more off-putting than flying along in a Korean war era Sabre, for example, and bumping into a flight of Ju-87's somewhere, lol - or vice versa, flying in a Hurricane, and suddenly have some Mig-21's on your case.
your choices here are twofold - the easier way is to simply not fly those missions that have these extra unwanted planes.
the second method requires you to gain a bit of knowledge in working with the FMB, where you have to open this QMB mission from inside FMB, and then go and look for, and delete, any extra flights in the mission.
just beware, editing QMB missions is a little trickier than a regular mission, so i'd advise first reading up on what specific requirements there are for QMB missions.
anyway, for now, this should help you to know what's going on with your QMB mission, why you're seeing these extra planes.
as i said, it's quite a common thing, something i personally dislike, but others like the extra planes.
i simply edit my QMB missions to not have extra clutter, if i want to fly a more immersive mission with loads of extra planes and stuff, i just fly a regular mission or campaign. QMB should be what it is, imho, Quick missions, with no extra frills.
cheers, and happy flying!