Quiet road alternative. A big hill to start with but after that can be fairly easy with good views of the loch.
Leave Fort Augustus on the B862 at the south end of the town. This is flat for a mile then there is a long steep climb. There is a flat section by pretty Loch Tarf then the climb begins again, finally there's a long descent with good views to White Bridge where there is a hotel doing morning coffee, bar meals etc.
The section between White Bridge and Foyers is very pretty, passing through natural pine woods. Remember to turn left on to the B852 a mile after White Bridge. There is a friendly tea room with home baking in Foyers.
After Foyers there is a rapid descent to the shore of Loch Ness. After Inverfarigaig you can if you wish simply remain on the B852 all the way into Inverness. This avoids most of the hills; the remaining nine miles by Loch Ness are very similar to the three you've already done from Foyers.
A more interesting way however is to take the first right after crossing the River Farigaig at Inverfairigaig and cycle up towards Loch Duntelchaig (this is not the steep road south of the river). Going this way you pass a series of lochs, all very pretty and also get good views high above Loch Ness looking across to the hills on the other side.
Most of this route is on very small back roads and is not signed. It is however not difficult to navigate if you count the lochs and the turnings. Most of the roads on this side of the loch run into Inverness using quiet back streets. Do not remain on the B851 as this will take you to the A9 dual carriageway at Daviot.