Marine Corps question...?

Hi. I am using my older brothers profile to ask thi, lol. Anyways, I am a little lost in life. I am 17, and have considered the Marine Corps for a while now. Problem is, I am generally a failure in school. I have the credit requirements to be a Senior next year, but I haven't received a grade higher than a C in 4 years. I routinely pull off 1.666-0.833 GPA's and I don't even think I have the overall 2.0 GPA requirement to graduate. I have no college ambitions. Not even at the community level. I am a tad bit out of shape, but I can fix that. I (hopefully) graduate in 2011. I have always wanted to join the Marine Corps, but now the recruiter has been telling me about the DEP and all that jazz. I haven't taken the ASVAB, and suck horribly at math. I want to join the Marines, but is it the right move? My parents refuse to co-sign the contract, so I have a while to think about it. I live in San Diego (a few blocks from MCRD), so "homesickness" would not be an issue. Once I take that oath, there is no turning back. My recruiter (like most of them) wants me to join as early as possible. Once I take that oath, there is no going back. Is the Marine Corps the right move?