Yes, unless the judge is willing to designate the offense as a misdemeanor nunc pro tunc -- meaning postdating the misdemeanor designation to before your possession of the gun.
I'd suggest you see a competent criminal defense lawyer about this situation. It can be tricky.
You need to contact a competent criminal defense attorney at your earliest convenience. It might be possible that this can be resolved simply - but without looking at your exact paperwork as to what you pled guilty to originally, I can't say for sure. Please feel free to contact us if you have any further questions.
I have defended another individual on a similar matter in the past. What you would need to do is file a motion with the court on your original case, to which you pled guilty, asking to designate the offense a misdemeanor and backdate it to the date when you completed probation. The judge does have authority to do this. If the judge grants that motion you can file to have the new charge dismissed.
I HIGHLY recommend you contact a criminal defense attorney to represent you in this matter. It is serious and potentially complicated and is not the type of thing you should try to deal with on your own.
I, like the others hear, would be happy to help you out.