in my openion you should hold this btc of $100 USD and then sell it after its price up . in this way no need to any marketing risk like in trading .
This is probably the safest suggestion on how to make it increase in the amount you have without any risk involved.
That is probably the safest way but that is not the best way for growing them as the price might take a lot of time to increase so that would not increase just $100 to a larger extent as trading can, it is always better to trade that amount to make them grow gradually.