I can never be a force to reckon with.
The phrase is normally "a force to be reckoned with", not "a force to reckon with".
I would suggest:
I am not a force to be reckoned with. (A statement of fact)
I'm not, and I never will be, a force to be reckoned with. (Your opinion)
I will never be a force to be reckoned with. (Your opinion)
I wouldn't say "I
can never be..." in this case because it is possible that in the future, you might find that you
can be!!! Nothing is impossible.