Kacie, I typed out a really long answer to your question and then my computer crashed 
But in summary, the risk to the average person in that area over the whole five year period would be about 1 in 54,000 (which is coincidentally almost exactly the same as the risk to a person who's in London at the same time as a terrorist attack kills 150 people there). That's if you include the countries mentioned in my previous post, as well as every country other than China where an Islamist attack has killed civilians since 2014 (if you include China it becomes more like 1 in 88,000). Obviously the risk won't be the same for everyone everywhere (you're a lot safer in rural Iceland than you are in Syria), but the UK is safer than some countries and less safe than others so as an approximation it'll do.
It's also worth noting that only a very few (~5) terrorist incidents worldwide have killed 150 or more people in the last two years - one was the Metrojet crash, and the rest were nearly all Boko Haram attacks in Nigeria where the police and military aren't as well equipped to deal with them (during one of the massacres the army ran away and then tried to lie about it even happening in the first place). Even attacks where more than 100 people are killed are relatively rare, especially if you exclude attacks by Boko Haram who aren't currently operating in the UK. So unless there's a major change in the scale of terrorist incidents everywhere, the actual risk to someone in the UK is likely to be much, much lower.
That means the average UK citizen is about 160 times more likely to die in a traffic accident (lifetime risk) than in a terrorist attack under the circumstances Kacie suggests - so that answers your question too, Rooners 
OP, I'm really glad you did go and that you had fun. Hopefully that'll also make it easier if you're worried about similar events in future Checking where the emergency exits are is a sensible idea anyway, not even because of terrorist attacks but in case of a fire or some other unexpected event - so if anything you're probably safer now than you were two weeks ago!
DrSausagedog you are braver than me 
but probably also more sensible 
I'm sure the risk is still tiny, especially with all the extra security - I think I'd be more concerned about the potential closures/bad atmosphere ruining the trip. I hope you have a good time, anyway!