URGENT, Please help. Travel question.

Hi everyone! I have a question if anyone could please help me, I would be very grateful.
I'm an American citizen and will be flying out from Beirut, Lebanon to Romania. But, in February and then again in March I was denied entry into the UK. This is my first trip since. I just wanted to ask everyone on here if they can advice me if I will face any problems at boarder control there due to my past two travel experiences?
I will be going for eight days and simply to be spending Easter holiday with my boyfriend and his family.

Thank you!
Hope to get replies!

I would be very surprised if you had any problems at all.  They may ask about the marks in your passport but just be honest with the reasons.  You should be on your way in no time.   

Sorry, I don't have any experience that would be useful here.

I'd bring docs that address the reasons they gave you problems before. That might mean bringing proof of sufficient funds, proof that your life is outside the UK and you need to return for work or school, awareness of the visitor visa rules, or knowledge of a visa you might be applying for in the future (work, partner, student, etc).

Can't hurt to have extra docs with you, but be sure to have them in your carry-on.