MP+1: 226.5 BB (VPIP: 25.24, PFR: 9.71, 3Bet Preflop: 3.03, Hands: 103)
CO: 84.5 BB (VPIP: 33.33, PFR: 33.33, 3Bet Preflop: 50.00, Hands: 3)
BTN: 61.1 BB (VPIP: 52.94, PFR: 0.00, 3Bet Preflop: 0.00, Hands: 17)
Hero (SB): 200.9 BB
BB: 116.9 BB (VPIP: 25.93, PFR: 11.11, 3Bet Preflop: 0.00, Hands: 27)
UTG: 29.5 BB (VPIP: 35.29, PFR: 2.94, 3Bet Preflop: 0.00, Hands: 34)
UTG+1: 107 BB (VPIP: 76.47, PFR: 23.53, 3Bet Preflop: 0.00, Hands: 17)
MP: 89.5 BB (VPIP: 28.57, PFR: 0.00, 3Bet Preflop: 0.00, Hands: 7)

Hero posts SB 0.5 BB, BB posts BB 1 BB

Pre Flop: (pot: 1.5 BB) Hero has 7 7

UTG calls 1 BB, UTG+1 calls 1 BB, fold, MP+1 raises to 5 BB, fold, fold, Hero calls 4.5 BB, fold, fold, UTG+1 calls 4 BB

Flop: (17 BB, 3 players) 4 3 K
Hero checks, UTG+1 checks, MP+1 bets 10 BB, Hero calls 10 BB, fold

Turn: (37 BB, 2 players) 5
Hero checks, MP+1 checks

River: (37 BB, 2 players) 8

His cbetting % was 90 btw

after flop you have completely lost control of this hand , but you're not bluffing here by thin valuing the river given turn action

I was rep straight or flush on river. I generally check in that spot on turn whether I have flush/straight or hand like I do. Is this wrong?

Should I be leading out when I hit flush/straight on turn and then mixing in hands like my 77?

77 is too high in range for a bluff, unless you are deep and jam river. Normally you would check this river or bet thin and villain will either bluff with AQ or showdown a weak pocket pair, maybe a passive Kx. Sure you can lead with a bet, but that is thin value and not a bluff.

Bluffs are hands with very little showdown value, such as high card or busted draws.

XC flop is not bad versus high freq c-bet villains, but you often have to hero call a larger bet on the river, so keep that in mind on the flop.

You certainly can bet-fold this river as played. However that is a thin value blocker bet, not a bluff. (I do not recommend this btw).

Just because we do not want to be called, does not make our hand a bluff, unless we are making a very large polar all-in jam.

flop is meh, passive guy bets into whale + reg with whale to act. Unpaired hands have 2 live outs etc
check river and hope to win showdown