You could try it. You could win.
However, the officer can also amend the citation to either:
(a) reflect another violation such as disobedience of the Road Closed sign. You lose.
(b) include the speed, timing device, etc. - He/she likely kept notes on the back of his copy of the ticket. Most officers do. In which case, you may lose.
(c) amend to 3361 (because any speed on a closed road would be too fast). You lose.
With a ticket worth 25.00 plus costs and carrying no points, you will have to decide whether it is worth it to see if you can convince a judge (who likely is not a lawyer) to find you not guilty.
As Mr. Morgan stated, you may have a point on the 3111(a), but the officer is likely to come out on top in the end. Quite honestly, he gave you a break by not citing you for a more specific offense. Had he cited you for a moving violation, your insurance rates would rise.
3111 is failure to obey a traffic control device, like a road closed sign, or any other sign for that matter. Small fine, no points on PA license, points in some other states though if you were only visiting PA and have an out of state license. I'd pay the $100 and be done with it if I were you. Too much to risk.