Well there are a few things you can do to address this.
I know its obvious but practise your scales and arpeggios. A lot of what you will sight read will include strings of consecutive notes from scales or arpeggiated chords. If you have practised these you will be surprised how quickly you "fall into" the correct fingering when you encounter those sorts of passages.
Also the more you play the more you will become familiar with the "normal" ways of playing certain passages. It seems a bit surprising at first (although less so if you think about it) but there is a lot of repetition in music between pieces. Apart from scale passages - which are all over the place - there are common chord progressions and other shapes for example the Alberti bass (look it up if you don't know what it is). These things appear again and again and after a while you will get so used to them you will, as with the scales, find yourself just using the correct fingering without thinking too much about it.
The previous paragraph can also be applied in other areas. Take the ornaments and embellishments in baroque music (Bach for example). You should find that having managed to work out how to play all the turns and trills in one thing (one of the Bach Partitas perhaps) you find similar embellishments in many other pieces and they will present less of a problem.
And, of course, just play. The more you do it the more familiar it becomes. The more you do it the more familiar it becomes. You can do this. Go for it.