how would I have earned 18700. Wish I had bought share on Friday and sold today?

Wish I had bought share on Friday and sold today? 

I am a trying to understand the stock market and trying to write my thoughts as a blog. Stock market is very volatile. I am a new bee and I am tracking some shares and one of it is share price. I noticed the price on Friday and it was 186.80 at 1 pm. If I had invested and bought two hundred share of and sold today I would have earned profit and price of today was 205.50

So I was thinking how much shares should I have bought 

If it was one share 

No of share *buying price = (selling price - buying price) * number of shares

1*186.80= (205. 50-186.80 )*1 i.e.,  18.7 rupees as profit.

So I had bought 10*shares then it would be

18.7*10= 187

18.7 *50=935

18.7 * 75 = 1402.5

18.7*100 = 1870

18.7*101 =1888.7

18.7*110 = 2057

18.7* 125 =2337.5

18.7*190 = 3553

18.7* 210 = 3927

18.7* 275 = 5142.5

18.7*350 = 6545

18.7* 401 = 7498.7

18.7*445 =8321

18.7*500= 9350

18.7*1000= 18700

So for 1000 share I would have earned 18700. But here my greed does not end what if tomorrow again the profit might go upto 23 or 50 then should I wait hold or book profit?

What happens if it goes down or up??