If I was you I would invest a higher amount or gain more bitcoins by as a example signature campaigns.
But you don't have to invest if you are going to gain more with the use of signature campaigns. I think the only way to make money with $100 btc.
Is by trading, just buy a lot of good alt coins with that amount.
And for sure you are going to get returns from it or if not, by just simply holding it and wait for a price increase.
Yeah many people really suggested trading since it was the only realiable platform where we can earn really big moneys by trading alts but we really need a good strat and patience so we can get more profit if price boost up high for more and also we cannot lose money if price go down deeper as we expected because trading is also risky if we dont really be mindful and carefull in buying some coins.