I have the same machine, or at least very close to it!
Mine is a Kenmore purchased in 2001, and it's 385.12312. (So one of the rebranded Janome's). If you have the same machine, or even a similar one - you SHOULD be able to drop the feed dogs. Embarrassingly enough, even though I've been sewing on it regularly for over a decade, I didn't realize it myself until recently!
If you open the cover to the bobbin case, and look on the right hand side next to the bobbin case, do you see a metal lever and some icons that look like little hills? That's the lever to drop the feeddogs. If you pull out the metal lever and shift it to the right, that'll drop the dogs....mine are a little stiff (from not using it for over a decade :roll: :lol: ) so I have to stick my finger behind the lever and give it a push to get the feed dogs to pop down. To pop the feed dogs back up, just shift the lever to the left again (you might have to stick you finger behind the lever to push on the side of the dogs). Amazing what you find out when you actually READ the manual. :oops:
Also, with my practice swatches, I would get loops like yours on the bottoms if my top tension was too loose. I can always tell if the thread tension isn't right, as the machine sounds like it's straining. I find I need a tension of 5 with the walking foot and about 4 with the darning foot, but ymmv.
One more thing.....if your machine ever starts sounding whiny or grindy, or like it's eating up the bobbin thread, it helps TONNES to take the whole bobbin casing apart, clean out all the dust/lint and rethread the whole thing. I keep trying to convince myself I 'need' a fancy new computerized machine, but it's amazing how well my little Kenmore sews if I just clean it out once in awhile - purrs just like new. I've never had it serviced either. That's the beauty of the older mechanical machines, you don't usually need a shop when you have issues.
Hope this helps!