ITA with
JuliaSB .... You've identified the problem as tension, but have not dealt with it!
Tension can be scary, only because we have been given that mindset that we should fear adjust it! Your top/bottom threads should meet in the middle of what you are sewing. So? identify whether the top needs to go down to the middle, or the bottom up towards the top. That will tell you what you need to adjust. Then do it!
Go ahead ... you can do it ... and conquer that fear!!!!