Hi, quick question that i couldn't find when searching, legendary weapon pack weapons, are they meant to scale with your level?

Reason being i managed to get an immortalius from the cash shop whilst level 9, but now at level 11 my weapon still have (lvl 9) next to it. will this become useless after a few more levels and should i have waited to spend my platinum once I'm a higher level? or will its stats increase with me?

Thanks