Straight, but oh no!

[iheartponeez]

15/3.8/INFINITYYYYYYY over 26 hands.

PokerStars No-Limit Hold'em, $0.25 BB (5 handed) Poker Stars Converter Tool from FlopTurnRiver.com (Format: 2+2 Forums)

Hero ($34.50)
Button :#A500AF(Villain)/ ($43.45)
SB ($18.40)
BB ($18.80)
UTG ($56.45)

Preflop: Hero is MP with 5[img]/images/graemlins/diamond.gif[/img], 5[img]/images/graemlins/heart.gif[/img].
<font color="#666666">1 fold</font>, <font color="#CC3333">Hero raises to $1</font>, Button :#A500AF(Villain)/ calls $1, <font color="#666666">2 folds</font>.

Flop: ($2.35) 6[img]/images/graemlins/club.gif[/img], 7[img]/images/graemlins/club.gif[/img], 8[img]/images/graemlins/diamond.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $1.75</font>, <font color="#CC3333">Villain raises to $4.5</font>, Hero calls $2.75.

Turn: ($11.35) A[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
Hero checks, Villain checks.

River: ($11.35) 4[img]/images/graemlins/heart.gif[/img] <font color="#0000FF">(2 players)</font>
<font color="#CC3333">Hero bets $5</font>, <font color="#CC3333">Villain raises to $15</font>

A-buh?!

Now what the heck? Where did I screw up and do I call?