Tomato leaves curling in an upward direction are a sign of either heat stress, drought or too much nitrogen. At this time of year, I suspect too much nitrogen, but the plant will adjust to this extra nitrogen. As long as it is only a few lower leaves do not worry.  Most likely that one plant is in a spot where it got a bit more fertilizer than the others. You can look forward to tomatoes this summer. Keep growing, Marianne Binetti