First off, let me ask this. Where are the scratches? If they're located on the backside of the bass that's to be somewhat expected - belt buckles... I wouldn't really worry about anything on the backside, there's really no stopping it. If they're on the front side of the body you could probably swing by a hobby shop and pick up some wood paint (no guarentees it'll be the exact same color as original finish due to fading or special blends) and wood putty.
Before starting your repair make sure all strings, bridges, pick-ups, or knobs are out of way or protected! Wipe down area of repair with a guitar cleaner and NEW guitar wipe!!
1. Fill the scratches with the wood putty and let harden.
2. Once dry, sand putty smooth to the rest of the body,
CAREFUL!! sand gently and caustiously, don't be an idiot and creat more scratchs...
3. Wipe bass down to remove any dust and make sure bass is completely dry.
4. Apply first coat of touch up, often this coat will be very light, almost see through. Make sure you apply paint very thin so final coats are not elivated above rest of body. Once first coat drys, wipe down area and apply second coat. Repeat 2 or 3 more times depending on how thick your coats are.
5. Use a clear finger nail polish or a paint clear coat as the last coat and that should give you a shiny finish assuming that's what you're original body has.
Once you're all done it should look ALMOST good as new, assuming you found an exact or very similar paint color. My other suggestion is to just keep the scratches, shows character and can tell a cool story (show damage) unless you weren't being careful and ran into something
I cringe every time I see a guitar/bass touch something other than a stomach, fingers, guitar stand, or case...
Let me know how it goes if you give my advice a shot
