Ok, first of all let me tell you that there are no rules in how to masturbate...pulling your skin back is not a must...you do it as it feels comfortable to you!
Pulling your skin back should happen when you are in the shower cleaning yourself. pulling your skin back should happen after masturbation to clean the area well.
Paraphimosis, which you are worried about is caused by poor hygiene or a direct injury, and does not require and erection to feel the pain. Your said you had no problems pulling your skin back when you did not have and erection....well then i don't think you should worry yourself with paraphimosis
BUT, if you do experience pain then you should go to the doc.
Also, you say that the forskin now feels strange, well that might be because you have not been doing so before and it just needs a getting used to.
I'm sure you are ok and good luck!!!
I forgot to mention that my foreskin now feels strange once i pulled it back