So let's quickly analyze how well Tunnel does at getting to Colonies.
First, if you're not buying Platinum at all, it does a pretty bad job. You need hands of 4 Gold, 3 Gold + 2 Copper, or 3 Gold + 1 Silver just to make $11. Given that you have 7 Copper and 3 Estate in your deck that you can't get rid of, plus however many Tunnels in your deck that you needed to get that Gold in the first place, chances are you're not going to get $11 for Colony very often. It's in fact impossible to make $11 after a Margrave (though even with Platinum, it's pretty hard to match 2 Gold + 1 Platinum).
So you want Platinums, except that by the time you hit $9 more than once, it's already time to hit the Colonies. This is because Tunnel delays gaining Gold by ~1 shuffle, so you're also getting the Platinum at least 1 shuffle later, and by then the game is quickly approaching its end.
Disregarding the strategy itself, how could you have done better? The first is getting your own Margraves. If you have lots of Golds, it's easier to match them up with +3 cards, and maybe the +buy would be nice for you. It hampers your opponent if you hit a good hand. It does sort of conflict with Oracle, but your Oracles only gained you 3 Gold over the course of the entire game, which probably hints that Oracle is not a good Tunnel enabler on its own. Certainly had you aimed for Margrave instead of City, you wouldn't have felt so compelled to grab all 8 Tunnels, which further impedes your ability to get to Colonies.