Question about credit cards

Hey guys
I have a quick question regarding credit and credit cards. I have 1 secured credit card ($300 limit) with Capital One and a $12,000 car loan with Santander. I haven't made any late payments yet (I've had a credit score for 2 months). My credit utilization (according to credit karma) is 33%. I was talking to my girlfriend's parents, who have insane credit, and they gave me the advice to never use a debit card again. Only use your credit card, then pay off the balance. Problem is, my limit is tiny on my current card and it won't get increased for a while because it's a secured card. My girlfriend signed up for a student card (no security deposit) with Discover and got a limit of $1,000. Her score right now is about 670 where mine is 644. I was doing some googling and some places recommend you have multiple credit cards, so do you think I should get a student Discover card too? I hit a bad financial spot a week or two ago and almost maxed out my Capital One card (though I don't owe anything for almost a month now so I'll pay off the balance when I get paid in a week). Is it smart to get that second or a third card?

Thanks