I painted for years and it is not for the inexperienced. Especially white.
If it is just one spot, take it to a shop. They will prep it correctly and get the paint matched as close as as possible.
I could go on and on about prep and masking and but it would really be in your best interest to take it to a professional.
If you want it to be as cheap as possible, ask them to use a single stage paint. No clear coat is involved, but it will last a good long time. We did my daughter's e46 coupe in a single stage and it's holding up great. Alpine White!
That's my opinion but if you want to tackle it yourself, PM me and I'll give you a call.
