Hey, Milly ...
So the "winter training regime" didn't happen then?
The end of March is quite tight. If you trained 4 days a week, that's only about 30 training sessions before the run.
Having said that ...
If you can get up to five miles, then you can do thirteen.
Have a go at some interval training (the poncy name for ... run a bit, walk a bit, run a bit, walk a bit).
If you can manage two miles, then you can build up to five by the end of March. Running with a lot of other people, once you get to five miles, you'll ba carried along by the occasion. Remember, you can walk a bit. But, if you have to walk, then keep walking. Don't stop, because the blood will drain from your muscles, and they will cool down, and you'll struggle after that.
Have a play with mapometer.com or mapmyrun.com and plot a route of about two miles, and give it a go.
Tips:
Wear gait fitted running shoes.
Wear proper running socks (probably the best £12 you'll spend).
Carry water with you.
Eat a couple of hours before you run.
Carry your iPod and start to work out which songs match your running pace, and put them in their own playlist. If you don't know where to start, try some of mine ...
I Said Never Again (Rachel Stevens)
Electricity (OMD)
Breaking The Law (Judas Priest)
Bad Girl (ZZ Top)
Summer Song (Joe Satriani)
Surfing USA (Beach Boys)
Heatseeker (AC/DC)
These all play at 160bpm ... a decent running pace.
Next, if you speed up or slow down, DO NOT change your running pace. Adjust the length of your stride, but maintain the same stepping pace.
And when it strats to hurt, even in public, don't be afraid to shout ...
... "GRRRRRNNNNNNNHHH !!!!!!!"
Don't worry ... you won't hear yourself,