Berry Blast Pie

Well, I've always wanted to make a berry-only pie.  One day in the grocery store there was a large bag of various berries, strawberries (1 package), raspberries (2 packages) and black berries (2 packages) all ready to be used at their most ripe point for $2.  Who am I to resist?  The plan went into action...

A pie.
Of berries.
Whoa.

Unfortunately, the filling did not set as properly as I'd hoped, there was too much juice remaining.  But I learned that an all berry pie is not for me.  It was too much flavor, even with some ice cream to dilute the richness.  I also gained a wonderful, easy, quick crust recipe that I highly recommend.  No messing with ice cold water and cutting in fat just so...no, no, no, just beat this together and press it in.  I'd pre-bake it too, before filling.

Awesome crust recipe:
1 1/4 C flour
1 stick margarine
3 T brown sugar
1 egg

Press crust into pie pan, bake at 400 for 13-15 minutes.

Over the top, but unsuccessful, pie filling:
2 packages raspberries and 2 packages blackberries
1 package strawberries, sliced
3/4 C sugar
1 T lemon juice
3 T cornstarch
1/2 t cinnamon

I coated the berries with these ingredients, letting sit while the crust baked. 
Then added them and baked in the crust for 30 minutes.

Perhaps you can tell me where I went wrong?  It was just too much juice after baking.  Not enough cornstarch?  I don't know, but would value insight in case I ever venture toward baking a berry pie again.

Bottom line: keep the crust recipe, it's so easy and low hassle; ditch the berry filling recipe.  Sure was a pretty pie though.