What speakers are they? If they have 4 mounting holes you may have to drill a couple of holes to get them to fit. Or did you mean they don't go far enough back into the speaker hole?
So the problem is that there are only 3 holes on the door and 4 holes on the speaker? If thats the case, then you just need to make more holes so that it fits.
So the holes in the door are 1/2 a cm wider than the holes in the speaker? What kind of screws are in them Got any pics to help me see exactly what is up?
Wouldn't suggest using velcro dude lol. The plastic is pretty soft so you could just make a hole (using the speaker itself as a template, screw one screw in and push it back while you do it) with a bradawl and you're sorted. Thats what I did, just be careful not to slip, and I would suggest getting someone else to hold the speaker in place so you can use one hand to push and the other to hold the bradawl steady