Are My Vagina Muscle Contractions Normal??

A couple of months ago, I found out that I have vaginismus and have been seeing a therapist and have been trying excersizes (sticking the finger in) and I get to a certain point (circa 3 inches in) where it feels like I'm entering a new smaller hole.

I know this may sound stupid BUT

Is that the muscle contracting OR is that the part where the hymen is and where penetration can begin?

I think you may be touching your cervix. It feels similar to a donut in shape--like a round circle with a hole in it. That hole is the opening to your uterus, and you shouldn't be able to actually stick your finger through it (it's too small).

The hymen is very close to the opening of the vagina. If you have had sexual intercourse or use tampons regularly, your hymen is probably torn and has retracted very close to your vaginal walls, so you won't be able to actually feel it.

I think if you were actively having vaginismus, you would probably feel the vaginal walls contracting on your finger, rather than feeling a discrete hole like you describe.

What you are feeling further in is the cervix, a firm smooth circular part that protrudes into the vagina and in it's center there is a small hole. You won't be able to put your finger into that though.
the Hymen is much further down than the cervix. Look at some anatomic models (your therapist may have one) or at pictures to understand the anatomy better.