[deleted] depending on where you are, if you are in north america, chances are you are bound by kyc laws from telecom companies and your sim card has your identity associated with it. As soon as you put the sim in in the phone whatever IMEI you have could be associated with that sim and your identity. So.
What im saying is whether you should return or not depends on what exactly you want to achieve and whether you have access to anon sim cards.
Also even if you had a anon-sim and had an anonymously acquired imei, the imei could be tracked to your home location slowly over time as you use your phone at home. This last point however probably required targeted attention from intel agency towards the imei.
So now see if you need to return or not.