On your post there should be a small box in the bottom right corner that gives the options '50/50 payout', '100% payout' and 'decline payout'. The decline payout is self explanatory and I use it when I'm sharing something that isn't my work like a song or something.

Now here's where it gets tricky - the 100% means 100% Steem Power, and the 50/50 means 50% SBD and 50% Steem Power. It isn't possible to get 100% SBD
Next time you do a post look for that box. If you change it to 50/50 it should automatically set your posts to 50/50 afterwards, but double check just in case...

I to Made Same mistake in starting.