no matter how hard i push the air bubble won't go away and the screen protector i got was like 10 dollars.
There's probably dust underneath it, once dust gets on the screen protector it's very hard to get rid of but you can try with scotch tape and hope you don't introduce even more dust in the process (which is often what happens)
Also any time you're applying screen protectors it helps to apply from one corner, slowly peeling off the protective layer while applying with a plastic card and going to the opposite corner, the plastic card should be right up against the edge of the protective layer where you're peeling. And always wipe the screen thoroughly, then when you are ready to start peeling and applying, give it another thorough wipe just to make sure. And after wiping keep the screen protector above the screen at all times so it acts as a dust shield so hopefully dust won't get a chance to get underneath there.
It's best not to get dust underneath in the first place, but sometimes it's unavoidable (particularly with larger screens or screen protectors with very tight tolerances where you end up having to take it off and reposition it)
I find that if I get it on perfectly the first time it usually won't have dust under it but if I have to take it off to reposition it there will most likely be 1-2 specks of dust. Usually near the edge though so it's not a huge deal.