I'm pretty sure you've already shown them politely and professionally.
It's not like I flirted with them or was anything besides just being
friendly but I did offer my number to shoot questions about a project.
You didn't say call me sometime to "hangout" and you also said you didn't flirt with her, so it sounds to me like you're already doing everything the way you should be. Of course there's always a chance that someone will find you attractive and want to pursue a relationship with you, but that doesn't mean it's your fault. In fact, you might be over thinking things a bit, but if you're really worried about coming off the wrong way and want to be crystal clear that you're taken, then I do have a few suggestions that have worked for me.
Use social media to your advantage. I would say this is easily your best tool at your disposal. Nowadays most people I know who are interested in someone romantically usually seek them out on social media to check what their relationship status is. I understand not everyone is always comfortable putting who they're in a relationship with and want to have a certain level of privacy, but if you use Facebook you can modify the settings so that your status only reads "In A Relationship" publicly.
Another option is to use Instagram and post recent pictures of you and your partner together with captions that highlight how happy you are together. Even more obvious is to just post a picture of your partner alone and caption it with how smitten you are. Something like "love of my life", "soulmate", "better half". Again perhaps you are a bit more private and don't have a public instagram or don't feel comfortable with this approach, well then there's always the couple profile pic move. Posting a couple's pic of the two of you together is usually a solid sign that you're happy in relationship that most people would pick up on.
The sneaky notification option. A tricky way of letting people know that you're in a relationship is to have your phone go off while in conversation with someone you want to notify of your relationship status. Once your phone alerts, you stop momentarily to check and "pretend" to read a text from your partner. You then giggle, laugh, small etc. and verbally say something like "my girlfriend/boyfriend is so sweet/funny/hilarious". Just to be clear... the sneaky option is my least favorite option. It works, but it does take a bit of preparation and deception. However, it could be less deceptive if you read an actual text that your partner sends.
My favorite option and the one that I feel is most effective is to be explicit. Tell your friend straight up that you have a girlfriend. Now maybe you're not 100% sure your friend is interested and don't want to make assumptions and deal with the the awkwardness of having to be so explicit. Well then my advice is to be explicit by being "detailed". A good tactic that has worked for me every time is to attempt to make plans with a friend and when trying to schedule the best time, I use it as an opportunity to explain that I can't do such and such time because I have plans with my girlfriend on a conflicting date. My favorite part about using this approach is that it also gives your friend an opportunity to save face and walk away from making plans with you once they know you're with someone. In my experience about 90% of the time the friend will "coincidentally" not be able to meetup all of sudden. A similar approach is to actually invite your friend to a social meetup amongst friends and even let them know that your partner is there and they'll be able to meet them. This is a good way of giving your friend an opportunity to really be friends with you because you're letting them know that you want to be better friends as well as being respectful towards your partner.