Normally on a first offense theft you are not looking at jail time. Especially considering your lack of record. If you are lucky, you might be eligible for the theft diversion program. The theft diversion program is a weekend program you attend where they talk about the affects of stealing and other related issues. At the end of the program they give you a certificate of completion. At least here in Franklin County, once you have your certificate and agree not to enter Walmart for two years, they will dismiss your case for court costs (usually around $100.00 or so).
The diversion program is probably the ideal outcome, assuming again you are in Franklin County. Other counties may handle your case differently. Also be warned that Walmart may send you a demand letter asking for a civil penalty - they are entitled to this under the law.
If you have any further questions or would like to discuss your situation in more detail, feel free to contact me.