Unknowns again first lap, I won't even bother posting the HUD stats over 9 hands since it's pointless.

Better to jam or just call here since we're getting like 5:1 anyway...?
Is the original raise okay?

I think my bet sizing is just fucked. Can someone explain better sizing - with an explanation rather than just the $ amount, thanks.

PokerStars No-Limit Hold'em, $0.10 BB (7 handed) - Poker-Stars Converter Tool from FlopTurnRiver.com

CO ($9.50)
Button ($6.50)
SB ($3.80)
BB ($9.85)
Hero (UTG) ($10.30)
MP1 ($11.10)
MP2 ($6.85)

Preflop: Hero is UTG with K, A
Hero bets $0.40, 1 fold, MP2 calls $0.40, 1 fold, Button calls $0.40, 2 folds

Flop: ($1.35) J, 3, 8 (3 players)
Hero bets $0.80, MP2 calls $0.80, Button raises to $1.60, Hero raises to $4, MP2 raises to $6.45 (All-In), 1 fold, Hero calls $2.45