It looks like the engines you're using are the static kind which do not pivot to help you exert control over the ship. There's a slightly less powerful version that does, so try removing the Reliant engines and putting Swivels on instead.
And it looks like you have no reaction wheel parts. Try mounting one of those to apply steering torque to the ship.
When you put fins on it, where did you put them? Can we see a picture of how you were trying to use them?
Vanamonde's post in What Happens When You Exceed Active Kerbal Limit? was marked as the answer