You should be able to see your order on the portfolios tab page, although you might need to scroll down a little bit. There will be a heading Queued orders. If you select that, you will be able see your order(s) waiting to be executed. - you can still cancel it at this stage if you decide you want to
One thing to be aware of is if you set orders outside of market opening times, it will execute at a determined time which I think is between 9:00am and 9:30am for the UK market and will buy the stock at that price at the time. If you set an order during market opening times, it will attempt to buy it at that time. This may be something to consider as you will have more control over the price yourself.