Of course, white should lose. I don't know Macs but computers that can't see further than 3 moves don't care about things further out than that.
That's why the computer played without purpose and you were able to pick off those pawns and get a queen with so little trouble.
I didn't see any bad moves on your part but you were three pawns down with no passed pawns. Black should have let his pawn mass stay put and have gone after your queenside pawns. You would have not been been able to defend.
If you play a computer which is stronger, you will see that.
Starting from move 42. I was playing on the Mac version of chess with difficulty = +3 moves ahead and somehow won this. I don't get how the computer didn't win.
Can any advanced players give me tips on how I played? I've been trying to get better and know I made some mistakes throughout as white.