There are income limitations to contributing directly to a Roth IRA. If you are single and your modified AGI is over $161,000, then you're ineligible to contribute directly to a Roth IRA. Please reference this IRS document.
If you have an excess contribution, you can withdraw it by 4/15 to avoid the penalty (make sure you also withdraw any earning on the contribution). Or, you could contact Vanguard to recharacterized this a traditional IRA. See: What if I made an excess Roth IRA contribution because my income is too high?