I understand your concern. I'm still worried myself that the Trump administration may try to find some way to subvert the results of the election should he lose. And looking at the numbers, the odds of him winning fairly are negligible. He's incredibly unpopular, and presidents with net negative approval ratings never win re-election. Also, Biden has been polling far better than Hillary, being at or above 50% in several key states that Hillary lost in 2016.
2020 isn't 2016, and Biden isn't Hillary. We have an incompetent, egomaniacal, and deeply unpopular man-child as president. The abstract of a possible Trump presidency in 2016 is much different than actually seeing what it's like living under the Trump presidency. We have a more likable Democratic candidate this time around, and he's running against the actual reality of the Trump presidency. Trump won by the skin of his teeth in 2016. Even a modest shift towards the Democrats will net Biden a win, and it's looking like a pretty big shift will happen.
It's not just the trump administration that's a worry. He may be incredibly unpopular in terms of pure numbers, but those that do like him, REALLY like him. The threat of domestic terrorism from hardcore trump supporters should definitely be a concern too.