Ohhhh .... not good to be 'desperate' ... sometimes leads to hurry and thus error.
I'll begin the discussion by asking some questions ... some folks may not think important ... but they do make a difference in approach to upgrading, me thinks!
What platform? Linux (if so what flavor)? We know version of Moodle you have, but DB server is ? Version is? PHP version is? Database character set/collaton?
These come into play on 3.0.x to 3.5.0.
First, login to your Moodle and check environment ... update the component, then select the versions of Moodle higher than your 3.0.x to see what Moodle might say you need to do before going to that version.
The environment check doesn't check plugins ... the addons and themes. Find out if the additional plugins you might have installed are compatible with destination version. Use the 'moodle store' to find your plugins and see.
In general, am one that adhere's to the 'march method' (if site installed with or moved to using git). Others will say one can 'hyperjump' ... skipping versions to get to desired destination version .... fine just check plugins / themes and be prepared to deal with some un-knowns.
Think all would agree that it's best to clone what you have to another server and test the upgrade process there first to work through issues one might discover.
Know how to backup the site ... code + DB ... and should an update/upgrade fail, know how to restore that backup!
'spirit of sharing', Ken