Hey, congrats! You said it was your first year of doing 401K contributions, right? So, congratulations for making those contributions during the year and then for doing your own taxes and uncovering more ideas for how to optimize them in the coming years!
I thought I had my taxes pretty well optimized. Then I got married and didn't realize I should change our withholding (dual-income family), so we ended up with a $2,000 refund last year.
Then this year, we received a bump to our income from a small inheritance windfall and erred on the side of over-withholding since it pushed us into a higher tax bracket. Then we bought a house in the same year. Long story short, we're getting around $7K back (!!!!). As others have said, I'm not happy that I gave an interest-free loan to the feds (and, in turn, paid more in interest on my student loans), but I am excited that this money will advance my goal of paying off my student loan debt to the end of the school year instead of the end of the calendar year.
It has made me realize that my taxes can also be an area that I can optimize -- for a really long time, I was focused on just earning enough money and cutting my spending enough to survive! Now, there's a whole new game to learn how to play and it takes time to figure it out!