By default (it's a Towny thing), plots are of size 16x16 even if there's a house on it that occupies two plots. You'll have to claim the second plot as well.

Also, you asked--

can you be in 2 towns or just in one?

No you can't. Just one. But you can buy [Embassy] plots in other towns if you have friends who live in other towns. Each player can only have up to 4 plots total.

If there isn't an embassy plot readily available, you can ask the town mayor/staff if they can let you have one. That's how I got my OceanView plot