They usually have them pruned back when they sell them and will sometimes include a few short newly growing vines that are left unpruned. They will start vining quite rampantly later during the summer. Give it time.

Thank you Jenny! I can relax now.

There is a bush version called dipladenia. Its not quite like the mandevilla (vine) but the flowers are similiar. I have both. I have seen the dipladenia (bush) labeled as mandevilla in either walmart or lowes (I can't remember which) just last week. If you check out the gallery I posted a pic of the bush version for you to take a look at. If yours doesn't look like that then you have the vine.