I am not a lawyer, so do not take this as legal advice -- that being said, here's what I think about your question...
You're being paranoid.
Not just about yourself infringing on others, but of "protecting" your own ideas as well. This stems, bluntly, from a complete lack of understanding about what can even be protected and of how valuable or not something is, just because it's 'protected'. The symptoms are evident in the way that you think you're working around D&D rules by using different stat names, etc -- and in your being overly secretive about your own specific rules. If anything at all can be protected, its certainly not the generalities -- its the specifics, in concert. That is to say, using different stat names affords you none of the 'protection' you seem to think it does, and by not revealing your complete ruleset no one here can formulate any idea at all about how vulnerably you might or might not be to litigation. I'm not saying to never think about it -- certainly you can't just clone existing rules outright and get away with it unchallenged -- but protection of creative works doesn't typically afford each element in isolation (e.g. rules, archetypes, themes, a'la carte) protection, it generally protects the sum total of those things, possibly together with *specific* people, places, and things (that is, nouns that begin with capital letters.)
Besides that, you say it took you three years to develop -- so, either in those three years you've done something amazing with and around those rules, creatively, which serves as a moat around your castle (good); or, what you have isn't all that special and neither affords or deserves the protection you think it does (bad). Game mechanics of any kind, as a general rule, are difficult or impossible to justify protecting -- ideas alone are not afforded the benefit of protection out of hand, there are requirements that have to be satisfied first.
And even achieving your own special snowflake of a game, guess what? Anyone can sue you at any time for any perceived toe-stepping at all -- and to the degree that their allegations have any semblance of a reasonable reality at all, their charges will either be thrown out, force you to settle, or drag you through a trial. That's not just a threat, its a legal tactic that IP holders use *all the time* to keep would-be competitors out of their scrapyard -- sometimes the bark is just as effective as the bite.
Despite my hyperbolic tone -- there's no bad news for you here, unless by "not copying D&D" you actually meant "I'm TOTALLY copying D&D!" If you can put your game down in front of any role-playing group worth their salt and they don't immediately shout "Dude! This to totally F*cking D&D!", you're probably about as safe as you can expect to be.