Honestly aside from all the posts lol, you can keep the amp and the sub but you need to change the box.
You can go bigger so you need less power to get louder, but to big will make the sub sloppy.
Or find someone who is good at box building and try to get a 4th or 6th order made for it, you will see wonders out of it you would not have thought about.
Also even if the amp is weak, check for clipping and power drop. Adding another battery near the amp would save the drop issue as a bandaid solution.
Also jl subs are NOT SPL SUBS, They are sq SUBWOOOOOFFFEERRRRSSS!!! Made to blend well with music, not to break ya dick off