curveball with a 2sfb?

Today I was throwing some 2 seam fastballs with my dad (about 65 mph) and most of the time it did a curveball or splitter or something random that you couldnt control. It was cool at first, but now its just getting annoying. I want to throw it straight but it won't! I was inside so it wasnt the wind or anything, any explanations or ideas?

That's just part of getting better. work on your form and make sure you release the ball properly. I can generally keep my two seam direct and get the curve to go the way I want but now I've been working on my slider and having issues with throwing at a bad angle and hitting the dirt.