I'm sure your LO will be absolutely fine - a couple of weeks ago I (stupidly

) crouched down to say hello to my FIL's dog and needless to say she excitedly jumped up at me and I got quite a hefty paw in the stomach. Earlier on in the pregnancy I would have been a lot more worried about it, but after having my 20 week scan and the sonographer being really quite rough I was much more able to brush it off. (My LO had her head buried right down in my pelvis during the scan so the sonographer really had to dig around with the probe to get her to move, to the point that it really hurt and I actually told her so. I figure though that if that amount of pushing and prodding wasn't doing any harm, then a bit of a thump isn't going to).
Of course having a bit of a whack on the stomach still played on my mind a little bit until the slight discomfort afterwards had settled down and I could still feel LO kicking away, but as expected there was no problem at all. I think just trust your own instincts. If you're really worried or get any pains/bleeding then of course it would be worth getting checked out, but unless you had a really bad hit on your bump or fell directly onto your stomach I'd say that's pretty unlikely to happen.