First note that the first clip on your timeline sets your project's settings. Since your first clip is a title rather than a clip from your video, you're sidestepping that feature. So move all of your video up one track, drop a clip of your video at the beginning of your clip and let the program do its job. (Check Project Settings under the Edit menu to make sure it's matching your video's specs.) You can trim that first clip pretty short if you'd like, then move all of your video back down to track 1. But make sure your project settings match you video specs.
In some case this won't work. If your video is using an H.265 codec or some other codec the program doesn't recognize, it won't work. But don't worry about that right now. Just see if it does work.
Second, note that, even if you render your timeline, the preview you see in the Monitor panel is just a medium-quality preview. It may well look pixel-y. But id you want to see what your final video will look like, you'll need to Export & Share a sample of your video. Then you can judge if the quality isn't up to snuff.