I'm sorry, but my character should be a CR3. It would be easily blown away by any CR3, cept maybe rust monsters. Any Druid which doesn't use obviously broken spells would still, admittedly, do just fine against your character, but Wildshape should not come into this. A 5th level Druid still cannot wildshape into ANYTHING which will hit an AC of 31. Ultimately, it would come down to which spells the druid prepared, and I will not address venomfire, an extremely broken spell which, thankfully, none of my players have even found yet.
Besides, a 5th level fighter should also be a CR5, and wouldn't be able to hit a 31 AC without heavy optimization (18 str+5 BAB is only a +9 bonus, not nearly enough to hit reliably.) And, at that point, assuming 12 Dex and +1 Full Plate, Still has an AC of only 20 (assuming a THF). You can hit that 60% of the time. With a single class level. Meanwhile, this fighter, without some crazy +to-hit, can only hit you on a natural 20.
Ultimately, your character blows CR guidelines away. A 5th level Druid shouldn't even be considered a CR appropriate encounter.