Sounds like it could be too high a dose if you get jittery, been there at 30-40mg but 20mg + 10mg both extended release later in the day works really well for me.

Remember that the way Ritalin (methylphenidate) works is not by boosting dopamin but rather slow down dopamin uptake. You still need to create the first "spark of dopamin" yourself that then slowly snowballs itself stronger. I'd say you need to take it at least a few days to weeks to see an effect and learn how it affects you. Start at just 10 to 20mg. Otherwise try another variation of methylphenidate like concerta or medikinet.