Riven should win vs. Akali, but it's definitely not a free win. You're supposed to get yourself an advantage before she hits 6 and gets some of her ult stacks. After that she is very strong 1v1, but still manageable for Riven (I think)
Leaving lane to chase Shaco was probably a questionable decision. Unfortunately jungle invades are really cheesy right now with how difficult it is to clear. Jungle Shaco is a menace in particular because even if the team tries to react to his invades he can escape easily. And if he doesn't invade his ganks can be very troublesome. Warding the side of your lane vs. shaco may only help so much; the more dastardly shacos can just run up the lane with his stealth and box behind you. Warding Shaco's jungle as a team can help you at least keep an eye of where he is on the map though, and warding the river or bush when you push up can at least help prevent him from flanking you without using his stealth so he can't use it as a gap closer during the gank after you flash/dash away. Enough about shaco though.
When you auto attack the enemy champion you'll draw minion aggro (ability damage does not draw aggro). When playing aggressive as a laner, especially a melee laner, especially a squishy melee laner, you have to respect enemy creeps. Particularly the ranged creeps (their damage is hard to kite). There are champions that can power through minions with their sustain, beefiness, and AoE damage like Renekton. But if you are not Renekton (or even if you are) you play around creeps in 3 different ways. Last hitting, pushing slowly or pushing crazy fast.
Fast pushing is only if your champion can AoE creeps fast and you just want to scale and pressure the enemy into being unable to attack you directly in your creeps. Your champion needs a lot of creep damage so you can delete the wave and reset if it's too close to their tower. This is just for getting past the early first couple levels and sneaking an early recall for pots to make a tougher lane easier.
Slow pushing is the standard aggressive strategy. This is where you maintain pushing slightly harder than your opponent. This gets you slight experience advantage so you have windows with a level advantage. This also gives you more creeps than your opponent to fight on your side making trades easier. The faster the push the bigger your temporary advantage, however the shorter it lasts (the weaker their creep line the sooner yours hits their tower). This is what I would do as Riven vs. Akali. Push slightly faster, attack her when she goes near your minions to last hit and definitely go on her when you have a level above her.
Freezing is for when you really respect your opponents skill level and that of the enemy jungle and his ganking power. And it's more for ranged champions who can poke easier. This is smarter the less mobile your champion is. So when you play Xerath or Lux mid or something.
I'm talking about the 3 above regarding the start of the lane, level 1.
Also remember, you generally don't want to leave your lane or recall when your wave is bigger but not at their tower. It'll push on its own deleting your farm and exp. If you pushed the lane a little vs. Akali then left to deal with Shaco you might have lost a ton of EXP if she last hitted only. Ideally you push the lane into tower before recalling or roaming, to minimize farm loss. Of course if you're too low hp you can't always do that, and dying sucks.
