Yes, but you said you bought them a month ago...that's longer than 20 days. Ergo you are up that well known creek, without a paddle.
I've have good luck with the ones from petco/aquariumplants.com - I get them at petco as an impulse buy...its an adventure to see what plants you end up with. This last bunch was primarily Aponogeton Undulatas (as near as I can tell), and the first batch I had contained 2 tiger lotus's. Generally the larger, walnut sized/shaped bulbs are tiger lotus, so if you find their blister packs, sort through them til you find with with fewer bulbs that are walnut shaped.