There's a better way to do this, though it takes a little more time, and a handful of perfectly-reusable Jumbo Gem Clips (standard trombone-shaped paper clips).
Step 1. Cut out your blank form. This is a 7.5" x 4.5" rectangle of cardstock. A paper cutter will give you a more even edge than scissors, but it's not necessary. You could even use fancy-shape scissors on the long edges of the rectangle, to get a fancy top and/or bottom of your tube.
Step 2. Use a bone folder, or a ruler with a sharp (metal) edge, to induce a curl in your rectangle. Hold a short edge of the rectangle firmly in the center. Place the ruler parallel to that edge, as near to it as possible, and at an angle to the table. Press firmly with the ruler and pull the ruler towards the opposite short edge of the paper. This will curl the edge away from the edge you are holding. Turn the paper 180 degrees (so you will now be holding the curled end) and repeat. You may need to do this a couple of times to create enough roll to allow you to roll the cardstock neatly.
Step 3. Use your hands to form a roll from the curved paper. It should be about 1-1/2" in diameter, but it can vary depending on your hands and your needs. This will be just shy of two full rotations of the paper.
Step 4. Place a thin line of white glue along the open edge of the roll. Aleene's Fast Grab Tacky Glue works best, but Elmer's School Glue will do just fine, and it's child safe.
Step 5. Use paper clips to clamp the edges in place until the glue dries. Press down in the center (un-clamped area) to help the glue adhere there as well.
Step 6. Remove the paper clips. Your craft roll is ready to use.
By the way, given the potential for the spread of harmful bacteria, I would not recommend using actual empty toilet paper tubes for crafting.