well you are practically trying to trade or maybe we can call this  day-trading although you are choosing a big range with a big profit instead.
what you need to know is that trading is not just buying at some arbitrary (low) price and then selling at some other arbitrary (high) price. if it was that simple then everyone would have been rich by now. the hard part is choosing those two prices.

for example you have to ask yourself why you chose "18000 dollars /1BTC" as your buy price. and why you chose "20000 dollars / 1BTC" as your sell price.
if you don't have convincing answers to these questions then you should not trade.