I received a text message stating that this number is from Wal-Mart promo center, and that I have a 100 gift certificate waiting for me, is this legit???

No!

To reduce the number of unwanted email and texts you receive, use these tips:

Be careful about giving out your mobile phone number, email address, or any other personal information.

Read through commercial web forms. Some websites allow you to opt out of receiving email from partners – but you may have to uncheck a preselected box if you want to do so.

Check for a privacy policy when submitting your wireless phone number or email address to any website. Find out if the policy allows the company to sell your information.

Do not respond to unwanted texts or emails from questionable sources. Several mobile service providers allow you to forward unwanted texts by simply texting it to 7726 (or "SPAM") to block the sender. Check with your  provider about other options.

Use a "junk mail" or "spam" email filter.

https://www.fcc.gov/guides/spam-unwanted-text-messages-and-email

I received an email also saying I $100 Wal-Mart rebate? to call this number

If you are foolish enough to call that number they'll tell you to pay a small "handling" or "tax" fee before they can send out the $100 rebate. After you pay they'll send you nothing.