If you don't solder your flextrack around curves, there will be a kink at the joint. Sometimes, you can get by with it in HO scale, but in N scale, that kink is likely to derail the trains. I bet you can pick up a soldering iron for less than 10 bucks from Harbor Freight tools, or a 25W pencil iron (would be fine for N scale) at home depot for about 16 bucks.
If you can't afford that, maybe you can find a friend or neighbor to loan you one for awhile.
Kevin