I am to understand that you have not attempted to shoot this in-line. Not sure which model you have but as Raider2000
stated, you should attempt to remove the breech plug, if indeed it has one. Some in-lines do not. The charge now in place should not give you a problem but the fouling from the previous discharges, will. Balistol is good or Kroil oil and even Hoppes #9 plus. Give it a good soaking for a minimum of two hours.
Now, if you don't have a removeable breech plug, again give it a good soaking down the bore and pull it with your screw jag. Sabots are fairly easy to pull or at least easier than patched round ball. The good soaking should will make the powder inert. Wish I had a dollar for every miss-fire I've had to pull.
If you got a manual with this kid, see what they recommend. Most will and some don't.