Mazal tov on your upcoming marriage!
It is normal to take a bit of time to figure out how to comfortably perform bedikot. The fact that you can insert your finger is a good sign that there is no physical issue preventing you from performing bedikot.
We suggest using the softest bedikah cloths you can find; there are various types sold commercially. Try to find the ones made of a soft cotton knit fabric. Alternatively, you can cut up a clean white undershirt if you can't find the softer type.
Get in a comfortable position, either with one leg up on the toilet, or even lying down on your side if that works better for you. Relax and slowly insert your finger gently but firmly. Try to get your finger in until at least the first knuckle. You may slightly moisten the cloth with water to see if that makes it easier to insert. If it still is difficult, you may put some water-based lubricant on the vaginal area a few minutes before performing the bedikah. It is important to remember that the vaginal muscles may tighten if you are stressed or anxious, so do your best to relax before performing the bedikah.
Until you are more comfortable performing bedikot, you may reduce the number of bedikot to the hefsek taharah, and one bedikah per day during the clean days.
Please feel free to get back to us with any further questions.
B'Hatzlacha!