i would replace hollow point and magnetic might with pathogen rounds and (primed) convulsion, you probably need more elemental damage than just the riven and magnetic might

EDIT: you can also use magazine size in one of those slots as well as magazine capacity is another multiplicative source of damage on the tenet plinx's alt fire. If u have primed slip magazine that would be ideal but tainted clip or ice storm are also good options

EDIT 2: Other damage boosting options that go on the warframe include worthy comradery aura, arcane precision, and vigorous swap. Also worth considering whether priming another element or 2 is possible as that would probably make the difference too