I'm sorry! It's really hard to give you advice on keeping your frog healthy, when conditions are just not even close to what the species needs! I understand that you're trying to do your best on a limited budget, but in all honesty. . .he's not going to survive for long. Is there any way you can return him to the store until you will be able to get a new tank that is better set up for the needs of this type of creature? Even if the store won't give you credit at this point, it is better to save his life than to keep him, unhappily, in such a confined space for as long as he'll live.
Check Craigslist, they often have 10g tanks up for little to nothing - I often see them on Freecycle (in my area), too. . . you really DO need something bigger for the guppies, also. 5 gups in a 2 gallon is just unkind, to be frank.
I wish I had something more positive to say, I feel bad for you - but let this be a lesson learned. Research before you buy, and never trust the salesman at the pet shop. We've all made mistakes, it's what you learn from them that count.
Good luck, and let us know if there is anything else we can help you with - we're always happy to talk frogs (and fish)!