Looks like you have an 18/15 build, so you have 2 extra attributes and a few extra skill points not being used, you should plan for a level 30 build, and use a character calculator:
http://infinitum.dyndns.org/crpg/calc.htmI'd only go 4 shield (the 5 skill shields are not useable on horseback for the most part) and the elite cavalry shield/knightly heater shield, and knightly kite shield (think that's the name) are all great 4 skill shields. 2 and 4 shield skill is what I recommend for anyone who will be using a shield from horseback.
Also, 2 athletics is too low, as a hybrid cavalry lancer/1h/shield user I would suggest the following build (looks like you only want/need 5 riding/15 agility so I'll have you go 21/15 at level 30):
Level 30 (4 420 577 xp)
Strength: 21
Agility: 15
Hit points: 56
Skills to attributes: 2
Power Strike: 7
Shield: 2
Athletics: 5
Riding: 5
Power Throw: 5
Weapon Master: 5
5 athletics is pretty good for athletics, 2 shield skill isn't very good, but will protect you pretty well against projectiles (try not to use it very much for taking melee hits)
Actually this build is pretty fucking terrible now that I look at it. I can't really give you a solid build because you're not going to have enough athletics, or not going to have enough shield skill to be able to max out power strike and still have 5 riding, throwing and WM. People typically convert 2 skills to attributes at level 30 to get a strength and agility divisible by 3 otherwise you'd be 1 attribute short of being divisible by 3 in one category), but in your case, I'd recommend converting 2 attributes to skills so you have enough skills to go around (you're going to have extras, so I suggested putting into Iron Flesh)
Maybe try this build:
Level 30 (4 420 577 xp)
Strength: 18
Agility: 15
Hit points: 63
Attributes to skills: 2
Ironflesh: 5
Power Strike: 6
Shield: 4
Athletics: 5
Riding: 5
Power Throw: 5
Weapon Master: 5