Can you be charged with shoplifting if you have not left the store?

Yes, you can be charged with shoplifting whether not you left the store.  If someone takes took an item knowing that it does not belong to them and intending not to pay for it, then they have committed the offense.  In other words, the crime is complete once they have formed the intent to steal (shoplift).  Not leaving the store is irrelevant .  It is conduct that implicates a person.

Without more specific details of the circumstances surrounding all of this, it's hard to say more.  The fact is that you are right in wanting to retain an attorney.  Skilled counsel may be able to have the charge dismissed or win at trial.  They can also help to arrange "diversion" which is an  alternative sentence that would allow you to complete a special type of probation that would in turn leave you with a clear criminal record.

You should be ware that a for a petty theft is a misdemeanor, the prosecutor has the discretion to charge it as an infraction if the value of the stolen item(s) is less than $50. If you are charged with an infraction, no jail time can attach therefore a PD will not be appointed.  However, if it is charged as a misdemeanor, then since incarceration is a possibility, a PD may be assigned to your case. PD have huge caseloads but then again, they handle hundred of these cases and know the law inside and out.  It's up to you whether or not to accept a PD if one is offered.  However, there are local and state agencies, both private and government, that provide free representation to individuals who qualify.  Legal Aid is one of those services.  Also, you can check to see if there is a law school nearby to where all of this happened; they typically run free/low cost clinics that handle these type cases.  Additionally, you can contact the local Bar Association in your county; they may have a list of attorneys who will take your case "pro bono" (for free) or at least for a reduced fee based on your income/circumstances.