This Credit Card Mistake Cost Me $30

And I'm still annoyed over it.

In my early 20s, I lived in a city and didn't drive a car. Back then, my transportation costs were actually pretty minimal.

But these days, I do my fair share of driving -- namely because I've evolved into your typical suburban soccer mom, complete with a minivan that's perpetually littered with Cheez-It particles and granola bar crumbs. As such, I tend to spend a lot of money on gas.

But my gas costs, like everyone else's, have soared this year in the wake of the Ukraine crisis. In fact, at one point I had to take a serious look at my budget and consider some changes to compensate for the higher prices I faced at the pump.

Of course, in my world, gas is one of those unavoidable expenses. I need a car to get to most places, and because my vehicle is fairly large, it's not the most fuel-efficient. Those things that can't be helped.

What could've been helped, however, was that I could've been smarter about swiping the right credit card at the pump to maximize my rewards. Instead, I spent months passing up the opportunity to snag more cash back -- and I'm annoyed at myself for making that mistake.

The right credit card matters

Between January and June, I spent about $3,000 on gas. That includes everyday fill-ups, but also, the cost of a big road trip we took down to Florida and a few other weekend trips.

During that time, I used a credit card that gives me 3% back on gas because it's the card I make the bulk of my purchases on. But then I realized that one of my cards that I don't use as frequently offers me 4% back on gas. So all told, I collected about $90 in cash back rewards when I could've collected $120.

Now in the grand scheme of things, it's easy to argue that $30 isn't such a big deal. And to be fair, it's not even enough to fill up my car in full (thanks, extra-large minivan tank). But it's an annoying amount of money to lose for no good reason, especially at a time when everything has been costing more.

Lesson learned

It's easy to get into the routine of swiping the same credit card all the time. And to be fair, there are benefits to sticking to a single card, such as having an easier time keeping tabs on your spending and tracking your purchases.

But one of the main benefits of using credit cards in the first place is getting to collect cash back or rewards on your purchases. And so you might as well make sure you're taking advantage as best as you can by using the right card.

Meanwhile, if none of your credit cards offer a generous amount of cash back at the pump, it may be time to apply for a new card. While gas costs have eased over the past few weeks, they're still very high. And so it pays to eke out as much savings as you can get.