Bettas don't have to be fed everyday and their stomachs are as big as their eye. Just stop feeding the little fella for the next two days and see how things go.

(Some people drop a small raw pea to cure constipation but that's only if the tummy is still bloated after you stopped feeding it for a few days.)

In future, just feed bettas once a day - I usually give my betta three pellets a day OR three bloodworms a day. Sometimes I skip one day just to let my betta's tummy relax.