I just testing martingale gambling method.

This is my experience:
After 2 days of gambling I collected 1500 Dogecoins
After 3 days of gambling I lost about 2000 Dogecoins

So I lost because, I have 20x negative times in row.
I expected about 18x or 19x.

Anyway, can anybody tell me what is max negative times in row?
Anybody have same expirience?