If the goal is calming your nerves, the safest way to invest $3,000 in bonds is a short-term Treasury fund.
Vanguard Short-Term Treasury Fund Investor Shares (VFISX)
The good: Mutual funds consisting of U.S. Treasury bonds are the safest investments outside FDIC insurance at your bank. Treasuries are backed by the full faith and credit of the U.S. government. Using short-term bonds means you're less impacted by interest rate changes.
The bad: Short-term bonds have low yields (0.89%) - even lower than online savings accounts (1% at Ally).
If this is just to get you started in investing, a mutual fund holding U.S. Treasury bonds will be safe. Later on, you could migrate to an intermediate-term treasury bond fund, or total bond market fund.