You can either:
a) Buffer the flow even more with ornaments or plants, or
b) Just ditch it and get another filter. I gotta let you know that not too long ago a member posted here about a recall for a couple of Top Fin products because the filter is faulty. Not sure if the filter in their 3.5G tank kit is included, but you better go check!
EDIT: as a side note, you might want to ditch those plastic plants. They're going to rip the Betta's fin.
a) Buffer the flow even more with ornaments or plants, or
b) Just ditch it and get another filter. I gotta let you know that not too long ago a member posted here about a recall for a couple of Top Fin products because the filter is faulty. Not sure if the filter in their 3.5G tank kit is included, but you better go check!
EDIT: as a side note, you might want to ditch those plastic plants. They're going to rip the Betta's fin.