It is grammatically correct. It, however, doesn't mean what you seem to think it does.
What that sentence means is roughly, 'If I end up assisting you, please feel free to contact me', which doesn't make a lot of sense, unless you're requesting that they thank you afterwards.
Instead, you can say "If you believe I can be of any further assistance, please feel free to contact me.", which is perfectly acceptable to send to a prospective employer.
If you for some reason need to stay close to that structure, Papa Poule's suggestion of "Should you feel I can be of further assistance, ..." is also correct and acceptable.