You are afraid of showing off. I have had the same problem recently. I read in Sunan An Nasa'i a Hadith that stated that the Holy Prophet (saw) had once said that he was afraid of something for the Muslims much more than the Dajjal, and that was showing off in prayers. So you are right to be on edge about this. As you should be since the only real way to not worry about this is doing good deeds in secret. When you do something in public, don't do it to show off, but do it to demonstrate a good deed to others so that they follow and do the same as well. In this respect you can do a good deed in public and it would not be counted as showing off. This is why the Holy Prophet (saw) did things publicly. He was obviously not a show-off. He was a Prophet of God who was the greatest example for men.
So if you worry about showing off by telling others of something you did, then gear yourself towards saying those things by trying to get your family members to do the same. If you tell them you did something in order to be praised for it, then it is showing off. If you told them about it in order to demonstrate a good deed that they should do as well, then there is no harm in that. But don't let the feelings of wanting to be praised be in you while doing so. Because that could still happen.
In the end, always be cautious of your own behavior. Your being cautious of it is a good sign that you fear Allah. So i say keep up the caution. It is better to be on edge than to be lax about something. You keep yourself from falling into error easily that way.