Sigma help in the wrong lobby

I played on an alt account (my main is hovering gold 2/1 - plat 5) to play with my friends and this account has not placed in a hot while. we ended up playing in a wide match because of it as silver 3 to diamond 4. i would love some tips on how to properly play sigma as i dont think im that good and what i could improve on in general. This match actually pushed me to my limits and i think i did decent. [i was duo'd with kiri if it matters]. code is [5MGRE2]