What can you do wrong at Sit&Gos???

[Atropos]

So, I have finished 175 Sit&Gos and my results suck:

69 x 22s: +10.67% ROI, 39.13 ITM, +162$
97x 33s: -5.34% ROI, 27.84 ITM, -171$
9x 55s: +1.01% ROI, 33.33 ITM, +5$

Only thing is: I dont know why my results suck so bad. Now I ask you:

a) Is it all variance? Small sample size etc... but plz take into consideration that I have played 7777 Sit&Go Hands, and that must have some inner meaning.

b) Play in levels 1-3 seems to be easy. Weak-tight, bet 1/2 pot etc... I was tilting some time, I dont have good reads and on average I lose 2 Chips during the first 3 levels.
But this isnt too much, is it?

c) Most of the Bubble Play seems easy and straightforward. Pushing is pure math, calling is pure math. Maybe 10% Intuition because one cant compute while playing but still. Only thing I have problem with is:

1. If there are 1-2 limpers, I'm on Button with X BB, how do I compute it? I need to know there limping ranges, SB call range, BB call Range, Fold Equity for Limper 1, Fold Equity for Limper 2, chance to win when called, ICM calculation.

2. Same against a minraiser, 3BB-Raiser, 3BB-Raiser + Coldcaller etc... How do I compute this easily?

d) If you have a big/clearly above average stack in level 3/level 4. Should you use it to gamble in very marginal +EV decisions, or should u use it to wait longer and pick your spots when stealing bettter?

e) When you have a low/clearly below average stack in level 3/ level 4. Should you try to gamble since your Equity is low anyways and you dont have much too lose and can start a newer Sit&Go quickly or should you wait for a good hand and hope to win 2-3 coinflips to get back?