Can someone enlighten me please how is this possible?

I just did a test on lowest limits, at 2NL, 9 max ante games $0.01/$0.02($0.01) started with $23.02 on my balance, 9 table open at the same time, played total of 882 hands, after session balance was $36.82

During the session i declined all EV Cashout offers, also declined to run twice, i ran everything only once just to make sure on the graph everything shows accurately, so here is the graph:



It shows after 882 hands i won 17.84$

My balance difference after the session was +13.8$ (Started with 23.02$ and ended with 36.82$)

So 4.04$ must be a rake since i got +13.8$ instead of +17.84$, one of my table got a cashdrop around 0,5$ so lets assume, 3.54$ is the rake from 882 hands, 0.40$ per 100 hand, 0.4$ is 20BB

Did i calculate correctly? how can it be 20BB/100 rake? is this normal? Did i count it wrongly?

I think i even made a slight mistake on calculation, if i had 23.02$ starting balance and graph shows win 17.84$ which cashdrop isn't counted, 23.02$ + 17.84$ and + cashdrop 0.5$ so overall lets say if rake wasn't existed balance would be 41.36$ after session, but now it's 36.82$ so basically rake took about 4.54$ after 882 hands played, so it's 0.51$ per 100 hand which is 25BB+ lol

How is this possible?

Sample size is too small. You ran hot and won 9 stacks, so you paid a lot in rake. Keep playing and it will get lower. Rake will still be high on nl2, but not this high.

You should also do this after you know how much of that you will get back

Your being results orientated. Come back after 100k hands