As mentioned by others, being in the back seat is a very common problem that will cause sluggish turn initiation, or even a complete inability to turn. It tends to go hand-in-hand with relying on counter-rotational movements from the upper body to force turns. Do you swing your arms every time you turn? Turns happen too slowly, so counter is introduced to speed them up. The result is a flailing, unstable posture with imprecise edge control that can result in a slam. If this sounds like you, focus on keeping your arms relaxed and close to the body and utilizing torsional flex to initiate turns.
If that isn't the problem, one other common source of edge catches at this level is simply trying to change edges too soon/quickly. If you try to change edges while you have any component of sideslip, you will catch your edge every time. Try to release the old edge smoothly and try to get the board flat before smoothly engaging the new edge.
As a beginner, the safest time to change edges is parallel to the fall line. You will gain speed while doing this so make sure you're comfortable enough with that to stay out of the back seat. From the old edge, steer the lead foot down the hill by allowing the downhill edge to drop closer to the snow. The board will twist slightly (known as torsional flex), and the difference in edge pressure will cause the nose to drop downhill. As you approach the fall line, release the edge pressure from the back foot as well. You should now be pointed straight down the hill with the board flat. Before gaining too much speed, gently apply pressure to the new edge, front foot first (more torsional flex), then adding the back foot after the new turn is established.
As you become more proficient, you will be able to safely change edges earlier in the turn. This is nice because it gives you speed control earlier. Listen for the board to get quiet. If you can hear skidding, don't change edges. Again, your board must be travelling tip to tail, or tail to tip (no skidding), to safely change edges.
Good luck, I hope you find this helpful!