I'm on a diet? Would it be ok to eat this late?

I'm 16. This morning I power walked/jogged 4 miles for an hour. Breakfast I had toasted whole grain cereal with fat free milk lightly sweetened with splenda. Lunch I had 1 1/2 bologna sandwiches. And for dinner I had a pack of peaches and cream instant oatmeal. And a few hours afterwards I power walked for 10 min on the treadmill (with incline). Would it be ok to eat another sandwich tonight? Would it ruin my diet if I did? Oh and how many calories was this? Thanks =)