Not knowing the law about weapons being concealed is no defense, as you found out. Unless there is more to the story, an appeal is not likely to prevail.
The main grounds for appeal are that the lower court 1) made a serious error of law and/or (2) allowed a verdict in the trial or entered a ruling or judgment that was against the weight of the evidence.
Your post suggests no valid argument on these kinds of topics.
Good luck to you.
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If you represented yourself and entered a plea (and even if you had an attorney), but it turns out you were factually innocent of the charges [meaning that the knife was legal and carried in a legal manner], you should contact a good criminal defense attorney in Visalia to look into a motion to withdraw your plea. You've got to act quickly or you may not be able to withdraw your plea and you'll be left with more complex appellate proceedings.
You have 60 days from sentencing to appeal the judgment so if you want to do so you better do it soon. By the time the appeal is decided you'll be long out of jail. You could also just lump it and serve your time. With credits you'll do no more than 8 days in custody. Of course that will put a misdemeanor on your record (Sounds like it's already there) but you could later on get it expunged. 8 days is not much compared to a long appellate process which I would get into only if you are 100% sure you are right. The statutes regarding concealed weapons are long and complex and you may have missed something.