It is impossible to be too morally good. It is possible to over-think morality and as a result act immorally, but this is a completely different thing. If you think it is possible to be too moral, then this simply means there is a difference between the morals you claim to believe in and the morals you actually believe in.
For example, suppose you believe that it is conceivable that by being too moral, you end up causing the destruction of human life. Actually, I reply, this does not mean that you were too moral; in fact, given that you regard the situation where you act "less morally" but human life is saved as being more valuable than the one in which you act "too morally", this simply means that, according to your view of morality, the action (or set of actions) which led to the destruction of human life were in fact immoral. Either that, or the destruction of human life was basically an acceptable thing given the existing circumstances.
PS. I haven't posted much recently. This was due to a) going on holiday, b) getting a new laptop and spending far too much time playing Civilization V after being unable to do so on my old laptop, c) writing a post about relationships and then removing it after deciding that there was too much detail that I did not think I ought to make public, and d) writing a post about money and altruism, then wondering if it was actually saying anything in the slightest bit original or non-obvious. The first reason no longer applies; I still play Civ V but the binging which occurred after ten months of deprivation is out of my system; and I do not regret removing posts which I do not feel actually have anything good to say. Basically, I apologise for my absence and hope to get back to a regular posting schedule.