If you were making $9.25 at your first job, why did you leave it? Were you aware that you'd be making $2.00 less an hour when you first hired in at this second job? If so, why did you agree to it? Why not find a job that matches what you were making before? You did mention that the $7.25 was JUST for the first 30 days - as in it acts as sort of like a "trial period". What happens AFTER that? What will you be making after the first 30 days? If it's close or right at what you were making before, I say deal with it and stick it out. You're only 17. It's great you're already working, but I highly doubt you have any major expenses to worry about, so if you make less money for 30 days, that's not all that big of a deal, is it?
Btw - $7.25 is NOT "free". It is the set minimum wage in several states (but yes, there are some that are higher too). Think about "tip jobs" - most of those make LESS than minimum wage because they get to keep their tips (or at least split them up with their co-workers they shared their shift with). For a 17 year old, $7.25 is definitely better than nothing. It would suck A LOT more as an ADULT when you have greater responsibilities and bills to pay.