On your iPad check Settings>Mail,Contacts,Calendars>Default Calendar. If you have multiple accounts listed, be sure you have selected a calendar listed under you iCloud account as your default (and not a calendar listed under something else like On My iPad, On My PC, Google Calendar, and exchange account calendars, etc). If you haven't, make this change then enter a new calendar event on your iPad and see if it syncs properly now.
If your settings are correct and your iPad is still not syncing new calendar events to iCloud, go to icloud.com from your computer and enter any missing events from your iPad calendar that are not on your calendar on icloud.com. Once your calendar on icloud.com is up to date, go to Settings>iCloud on your iPad, turn Calendars to Off, choose Delete from My iPad when prompted, then after a minute of so turn Calendars back to On. Then enter a new event on your iPad and see if it syncs to icloud.com properly now.