Are the joins over lapping, or are they too wide? If they are over lapping, you can sand the over-laps off & then re-paper. If the gaps are too wide, then you are going to have to re-paper. Try as you might, there's no really effective way to fill such a small gap. Sorry for the bad news.
Filling and painting over will show up the difference in texture between the paper and the filler. For best results, paper over, this time butting the joints carefully. A heavy grade paper will help hide the old joins.