Sounds like drift to me.
Some people use a rounded cylinder as a fence, which is the "single point" that @FrankC
mentioned. You draw a line across the top of your board, then adjust the angle to keep the blade on the line as you make the cut.
Other people try to measure drift, and adjust the fence angle accordingly. Many bandsaw fences can be adjusted as needed. Do a web search to learn about that.
Bandsaws can be finicky. Not only could you have drift, but is the cut the same width at the top AND bottom of the wood? Is the tension right? Sometimes a bandsaw blade will flex as you push the wood, making a slight curve in the cut.
My bandsaw did not come with a fence, so I bought the Kreg model, along with both of their curved resaw guides:
After two years of owning that bandsaw, I still haven't decided which way I prefer: Fence or Fence-with-Resaw-Guide. It doesn't really matter as long as the cut is good.
I am also including photos of Rikon's bandsaw fence and their cylindrical guide. I grabbed them from Rikon's website.
If you want to try your own cylindrical resaw guide just see what happens, get a nice smooth piece of sprinkler pipe. Square it up to a board and attach it with screws from behind. Wax the pipe to make it smooth. Clamp the board to your fence. Give it a whirl.
IMPORTANT DISCLAIMER: I just made it up on the spot and have never tried making a resaw guide from sprinkler pipe myself, since I own perfectly good resaw guides. I hope the idea is a good one.
When you use a resaw guide, you place it so the "point" is just in front of the blade. Try 1/4 inch or so. Find what works for you.
Rikon's cylindrical resaw guide, and a closeup of the cylinder.