Hi Mowmow, i guess the first question has to be is the D/s side of things your kink as well as his/hers? Or is this something that you are trying to go along with to keep someone happy?.
If its not really your cup of tea initialy then submission is much more of a challenge, im sure your partner is very aware of the pleasures ahead if you can adopt the submissive mindset but you may be having trouble "seeing it" as it were, although i must admit taking someone who is not that way inclined naturally and converting them, although much more difficult, is very satisfying..
I had similar issues with my sub but you really do have to try to "let go"..
One way around it to enable you to commit fully to this is to agree to give in to it completely, and agree to keep an open mind, and if you trust your partner try to take the "try anything once" approach, but to enable you to feel comfortable keep a safety net in place that you will submit for a set number of weeks to allow yourself to experience different things a couple of times to see if you grow into them, to experience being set rules to live by and to adjust to the feeling of control, with the safety net in place you may feel more comfortable about trying things out without feeling llike its forever, then after the period you can sit down and say "liked that", "hated that never again" etc..And iron out something more long term that works for both of you....Letting go of the preconceptions and stereotypes that you may have been bought up to expect of a relationship is the key and you hopefully may discover a whole new way of living that feels more comfortable and natural than the old one, hard as it may seem to accept at this point