After following the tutorial, I got the weapon icon in the right place but I still have the old one floating there. I looked at old topics on this for at least an hour but I still haven't figured it out. (Probably I'm just really dumb ).

My extraweapons.hud: I'm getting these errors that appear to be related:

This error says that you are using Fragme!'s floating HUD icon fix with two or more of your sides which would result in your double icon problem. I personally do not have this problem because I munge one .lvl file for all my sides. In your case however, what I would do is, just with one of you sides set up an extraweapons.hud file. Copy all of your coordinates/postions into that one extraweapons.hud file alone. Then remove the references to extraweapons and com_inv_mesh in your other sides' REQs. Alternately you can munge a custom ingame.lvl and fix all of your icons that way via a custom .hud file. I hope all this makes sense to you.

It makes sense, yes.

But I've only tried fixing one side. I only have one com_inv_mesh and one extraweapons.hud.

When I tried a custom ingame.lvl, I had the same problem of two icons.