I'm partial to retaking/gap year cos that's what worked for me, gave me time to think on my future but its entirely up to you. If you do retake, make sure its a sixth with the same exam board or at least a similar one, do not fall into the same habits that caused you to get theses grades in the first place, get as much work experience as possible to make up for the retake, make it look purposeful. Goodluck ^^